
GopyiigMIs^l 



COPYRIGHT DEPOSm 



PRINCIPLES AND PRACTICE 
OF MILK HYGIENE 



BY 

LOUIS A. EXEIN, V.M.D. 

PHOFESSOR or PHARMACOLOGY AND VETERINARY HYGIENE IN THE SCHOOL OF VETERINARY 
MEDICINE AT THE UNIVERSITY OF PENNSYLVANIA, AND DEAN OF THE FACULTY 



U ILLUSTRATIONS IN THE TEXT 




PHILADELPHIA AND LONDON 
J. B. LIPPINCOTT COMPANY 






T 



COPTEIQHT, 1917, BT J. S. LIPPINCOTT COMPANY 



PalNTED BT J. B. LIPPINCOTT COMPANY 

AT THE WASHINGTON SQUAKE PKES8 

PHILADELPHIA, U. S. A. 



OCT 29 1917 



0CU477228 



PREFACE 

In this book an effort has been made to present 
systematically, in concise form, the facts and principles 
which are of importance in the practice of milk hygiene 
and to describe how they may be applied in the inspec- 
tion of dairy farms and in the examination of milk. The 
material has been obtained from various sources. Jen- 
sen's " Milk Hygiene," Savage's " Milk and the Public 
Health," Conn's " Practical Dairy Bacteriology," Swith- 
inbank and Newman's " Bacteriology of Milk," King's 
" VentHation," Van Slyke's " Modern Methods of Test- 
ing Milk and Milk Products," Grimmer's " Chemie und 
Physiologic der Milch," Kievel's " Milchkunde," Weig- 
mann's " Mykologie der Milch," Ernst's " Milchhygiene 
fiir Tierarzte," Sommerf eld's " Handbuch der Milch- 
kunde," and Barthel's " Methoden ziu* Untersuchung 
von Milch und Molkereiprodukten " have been freely 
drawn upon, while articles by numerous research workers 
which have appeared in the various journals and official 
reports have furnished many important facts. To all of 
these authors and investigators due acknowledgment is 
made. 

The book is intended primarily as a text for students 
taking a course in milk hygiene, but it is the hope of the 
author that it will also prove of service to dairy inspec- 
tors, milk examiners, public health officials, dairymen, 
milk distributers, and others interested in the production 
of wholesome milk. 

Louis A. Klein 

Philadelphia, Pa. 

September 15, 1917. 



Digitized by the Internet Arciiive 
in 2010 with funding from 
The Library of Congress 



http://www.archive.org/details/principlespractiOOklei 



CONTENTS 



I. Physiology of Milk Secretion 1 

Udder Structure and Cell Activity, Stages of 
Lactation. Phases of Milk Secretion. 

II. Colostrum 11 

Physical Properties; Chemical Properties; Micro- 
scopic Appearance; Ferments or Enzymes; Change 
from Colostrum to Milk; Judgment of Colostrum 
as a Food for Man. 

III. Milk 14 

Chemical Properties: Constituents; Variations in 
Composition; Reaction. Physical Properties: 
Color; Odor and Taste; Specific Gravity; Refrac- 
tion; Viscosity; Freezing Point. Microscopical 
Appearance of Milk and Milk Sediment: Cellular 
Content; Number of Cells. Biological Properties 
of Milk: Ferments or Enzymes; Original and 
Bacterial Ferments; Diastase; Peroxydase; Cata- 
lase; Reductase; Antibodies or Immune Bodies; 
Germicidal Action of Milk; Toxins; Aggressins. 
Classes or Grades of Market Milk: Certified Milk; 
Inspected Milk; Pasteurized Milk; Grade A; Grade 
B; Grade C. 

IV. Bacterla^ in Milk 50 

Common Milk Bacteria: Acid-forming Bacteria; 
Gas-forming Bacteria; Peptonizing or Casease 
Bacteria; Alkali-forming Bacteria; Inert Bacteria. 
Variations in Number and Kind of Bacteria: 
Original Contamination; Temperature; Age of 
Milk; Proportion of Different Groups of Bacteria. 

V. Milk Defects 66 

Milk Defects Which are Present in Milk when it 
Comes from the Udder: Cow-like, or Salty, Cow- 
like Taste; "Fishy" Milk; Rancid Milk; Slow- 
creaming Milk; Premature Curdhng; "Gritty" or 
" Sandy " Milk. Milk Defects which Appear After 
the Milk is Drawn from the Udder: Bitter Milk; 
Viscid, "Ropy," or "Stringy" Milk; "Soapy" 
Taste; Failure to Sour and "Butter;" Stable-like, 



vi CONTENTS 

Turnip-like and Beet-like Tastes, and a Burnt or 
Malt-like Taste and Odor; Blue Milk; Red Milk; 
Yellow- or Orange-colored Spots; Yellowish-green 
Discoloration; Greenish- Yellow Spots; Violet- 
colored Spots. 

VI. Influence of Disease Upon Milk 72 

Diseases of Cattle Transmissible Through Milk: 
Tuberculosis; Aphthous Fever or Foot and Mouth 
Disease; Cow-pox; False Cow Pox; Furunculosis of 
the Udder; Anthrax; Rabies; Actinomycosis; Milk 
Sickness or Trembles. Diseases of Cattle which 
may Render Milk Harmful to Man : Inflammation 
of the Udder (Mastitis); Blood in Milk; (Edema 
of the Udder; Indigestion; Spoiled Feed; Septic or 
Hemorrhagic Enteritis; Septic Metritis; Retained 
Placenta; Infectious Abortion; Other Diseases; 
Excretion of Medicines Through the Udder. 
Diseases of Man Transmissible Through Milk: 
Typhoid Fever; Paratyphoid Fever; Diphtheria; 
Septic Sore Throat; Scarlet Fever; Tuberculosis. 

VII. Dairy Farm Inspection 126 

Stable: Exterior; Interior. Cows: Examination 
for Cleanliness; Stage of Lactation; Examination 
for Symptoms of Diseases. Stable Practices: 
Method of Cleaning the Stable; Cleaning the Cows; 
Methods of Milking; Feeding; Bedding. Milk 
House: Location; Construction; Apparatus; Water 
Supply. Score Cards. 

VIII. Pasteurization 203 

Principles of Pasteurization: Effect of Heat on 
Pathogenic Organisms; Effect of Heat on the 
Common Milk Bacteria; Toxins and Decomposi- 
tion Products; Nutritive Properties; Ferments or 
Enzymes; Taste; Cream Line. Methods of Pas- 
teurization: "Flash" or Continuous Process; 
"Holder" Process; Pasteurization in the Final 
Container; Types of Pasteurizers; Biorization; 
Ultra-violet Rays; Electricity; Ozone. 

IX. Methods of Examining Milk 223 

Collecting Samples; Preserving Samples; Stable or 
Herd Samples; Individual Samples; Mixing the 
Milk Sample; Color, Consistency; Odor and Taste. 
Determination of Specific Gravity; Determination 
of the Per Cent, of Fat; Determination of Total 



CONTENTS vii 

Solids; Determination of Solids Not Fat; Deter- 
mination of the Specific Gravity of the Solids; 
Determination of the Per Cent, of Fat in the Total 
Solids; Determination of the Degree of Adultera- 
tion; Tests for Nitrates and Nitrites; Detection of 
the Usual Adulterations; Determination of the Re- 
fraction Number; Determination of the Reaction; 
Tests for Preservatives; Standard Methods of 
Counting Bacteria; Examination for Streptococci; 
Examination for Coli; Examination for Tubercle 
Bacilli; Fermentation Test; Estimation of the 
Number of Leucocytes; Boiling Test; Alcohol 
Test; Catalase Test; Reductase Test; Fermentation 
Reductase Test; Diastase Test; Tests for Heated 
Milk; Examination for Dirt; Test for Lactose; Ex- 
amination for Coloring Matters. 

Appendix 303 

Methods and Standards for the Production and 
Distribution of "Certified Milk": Organization 
of Medical Milk Commissions; Hygiene of the 
Dairy; Transportation; Veterinary Supervision of 
the Herd; Bacteriological Standards; Chemical 
Standards and Methods; Methods and Regula- 
tions for the Medical Examination of Employees, 
Their Health and Personal Hygiene, 



ILLUSTRATIONS 

FIG. HALFTONES page 

1. Alveoli of the Udder in Cross-section 2 

2. Cross-section of an Alveolus of the Udder at the Time 

of Parturition 2 

3. Involution of the Udder of an Old Cow 3 

4. Extremity of the Milk Cistern 3 

7. Colonies of Coli Aerogenes 54 

8. Colonies of Proteus Vulgaris 54 

21. Internal or Double-tube Cooler 186 

41. Various Types of Dirt Testers 300 

TEXT CUTS 

5. Preparation Showing Streptococcus Lacticus or Bacterium 

Lactis Acidi 53 

6. Preparation from Sediment from a Cow Affected with 

Catarrhal Mastitis 53 

9. Inlet in a Wall Already Constructed; Inlet in a Wall 

Being Built, and an Outlet Shaft with Two Openings. . 132 

10. An Outlet Flue Hinged at the Ceiling 134 

11. Cross-section of Stable Floor 142 

12. Window Arranged to Act as Fresh Air Inlet 147 

13. Open or Uncovered Pail 171 

14. Covered-top Pail with Opening Nearly Horizontal 171 

15. Covered-top Pail with Vertical Opening 172 

16. Another Variety of Covered-top Pail 173 

17. Floor Plan of Conveniently Arranged Milk House 181 

18. Cooler of Conical Type 183 

19. Corrugated Type of Cooler 184 

20. Tubular Cooler, v/ith Continuous Surface 185 

22. Section Showing Relation of Water Table to Surface Irreg- 

ularities 194 

23. How Springs May be Polluted by Subsurface Drainage. . 195 

24. A Pasteurizer of Simple Type 216 

25. Pasteurizer 217 

ix 



X ILLUSTRATIONS 

26. Pasteurizer 218 

27. Regenerative Cooler 219 

28. A Simple Holding Tank 220 

29. Retarder of the Tank Type 221 

30. A Combined Pasteurizer and Holder 221 

31. Quevenne's Lactometer 228 

32. Westphal Balance 232 

33. Modern Type of Babcock Milk-testing Bottle 234 

34. Pipette Used in Babcock Test for Measuring Milk 234 

35. Cylinder Used in Babcock Test for Measuring Acid 235 

36. Bottle and Pipettes Used in Gerber Test 237 

37. Feser's Lactoscope 239 

38. Zeiss Dipping Refractometer 251 

39. Sediment Tube Used in the Trommsdorff Test 283 

40. Gerber -Lobeck Catalase Apparatus 288 



PRINCIPLES AND PRACTICE 
OF MILK HYGIENE 

CHAPTER I 

PHYSIOLOGY OF MILK SECRETION 

Cektain facts concerning the physiology of milk 
secretion are of importance in milk hygiene. These will, 
therefore, be briefly presented. 

Udder Structure and Cell Activity^. — The udder or 
mammary gland of the cow consists of a large number 
of alveoli or acini arranged in lobules or groups and 
held together by connective tissue. The alveoli of each 
lobule communicate with a common duct which, after 
emerging from the lobule, continues its course in the 
interlobular connective tissue toward the milk cistern. 
The ducts from the several lobules unite to form the 
larger milk canals. The latter increase in size as they 
approach the milk cistern, in which they terminate. 
From the bottom of the milk cistern, a short, narrow 
canal, called the teat canal, extends through the lower 
end of the teat to the exterior. The udder of the cow 
contains four of these glandular systems, one for each 
teat. Each glandular system is spoken of as a " quarter." 

The alveoli are lined with glandular epithelial cells 
which, in the actively secreting udder, are separated from 
the capillaries by only a thin basement membrane. These 
cells select from the blood circulating in the capillaries 
certain materials which they convert into those substances 

1 



2 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

which are pecuhar to milk. They also take from the 
blood, water and other substances which are common 
to milk and blood. In histological sections, the milk fat 
may be observed within the actively secreting cells in 
the form of small fat droplets (Fig. 1) . The other con- 
stituents of milk, being without form, cannot be seen, 
but their presence in the cells is indicated by a granular 
or turbid condition of the protoplasm. When the cells 
of an alveolus become filled with secretion, the cell-pro- 
toplasm contracts and the contents is discharged into the 
lumen of the alveolus, after which secretion again begins. 
The different stages of cell activity do not occur in all of 
the alveoli at the same time ; different alveoli in the same 
lobule may show various stages. Secretion continues 
until the cells are exhausted, and it then ceases until 
the cells can recuperate. 

In the course of time, after repeated periods of activ- 
ity, exhaustion and rest, the epithelial cells of the alveoli 
are worn out and secretion stops in one alveolus after 
another. This change is called involution. In young 
cows the worn-out cells are regenerated. The alveoli 
then present the same appearance microscopically as 
is observed at the time of parturition (see Fig. 2) . The 
interalveolar connective tissue is increased in volume and 
contains many leucocytes. Leucocytes are also numer- 
ous in the alveoli, together with exfoliated epithelial 
cells, free nuclei, parts of disintegrated cells, fat globules, 
and coagulated casein. Fat droplets may be observed 
within some of the leucocytes. By their amoeboid move- 
ment the leucocytes migrate from the interalveolar con- 
nective tissue into the interior of the alveoli, passing 
between the epithelial cells; and the same movement 
enables them to take up fat droplets and carry them 




-A 



Fig. 1. — Alveoli of the udder in crosa-sectinn, showing: (A) fat-droplets in the epithelial 
cells, ( B) division of the nucleus, (C) a leucocyte in an epithelial cell, {D) epithelial cell with 
protoplasmic projection, alveolar content with (E) cells and (F) free fat, and (G) interalve- 
olar connective tissue. (From Cheniie und Physiologie der Milch, by Dr. W. Grimmer.) 




Fig. 2. — Cross-section of an alveolus of the udder at the time of parturition. (A) 
epithelium, (B) basket cells, (C) leucocytes, (D) nuclei of connective-tissue cells, {E) blood 
capillary. (From Chemie und Physiologie der Milch, by Dr. W. Grimmer.) 





f> : ' 






4i» 



''. ' 



*'♦. 



B. 









4\ 



(•'^ c 



Fig. 3. — Involution of the udder of an old cow. (A) epithelium, (B) leucocytes, (C) 
blood capillary, (D) interalveolar connective tissue. (From Chemie und Physiologie der 
Milch, by Dr. W. Grimmer.) 





Fig. 4.— (A) Funnel-shaped, (B) bell-shaped extremity of the milk cistern. (From Chemie 
und Physiologie der Milch, by Dr. W. Grimmer.) 



PHYSIOLOGY OF MILK SECRETION 3 

out of the alveoli. An alveolus which has undergone 
involution and regeneration remains inactive until the 
next parturition. As the period of the secretory activity 
of the udder advances, the number of alveoli in this con- 
dition increase and the quantity of milk secreted con- 
sequently decreases. This change occurs slowly in some 
cows and rapidly in others, and is commonly spoken of 
as "going dry." Usually the secretion decreases until 
it stops altogether; the cow is then said to be "dry." As 
the termination of secretory activity in the udder ap- 
proaches, the composition of the milk is considerably 
changed. Secretion of milk is also called "lactation," 
and the period during which a cow produces milk is 
called "a lactation period." 

As the cow advances in age, usually beginning with 
the fifth lactation, some of the worn-out alveoli are not 
regenerated. With each succeeding lactation an increas- 
ing number remain permanently inactive or break down, 
and the quantity of milk produced is consequently de- 
creased. The interalveolar and interlobular connective 
tissue gradually increases in volume, while the gland tis- 
sue decreases. ( See Fig. 3. ) Finally the udder becomes 
firm and hard and is said to be "fleshy." A similar 
change is sometimes caused by disease in young as well 
as in old cows. 

Stages of Lactation. — The function of milk secre- 
tion is intimately related to the function of reproduction. 
Pregnancy stimulates the development of the gland tis- 
sue of the udder and secretion begins a few days before 
or at the time of parturition. Why the udder begins 
to secrete at this time is not known. Of the many the- 
ories advanced, that of Schein appears to be the most 
plausible. According to this theory, the blood of the 



4 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

pregnant cow contains certain substances called "milk- 
forming substances." During pregnancy the greater 
portion of these substances is required for the nourish- 
ment and development of the foetus, but sufficient is 
left over to stimulate the development of the glandular 
tissue in the udder. When the foetus is developed, all 
are available for action upon the udder and secretion is 
stimulated. 

At the time of parturition the udder does not secrete 
milk, but a substance called colostrum. The alveoli at 
this period contain many cells, entire and disintegrated, 
and leucocytes are also numerous in the interalveolar 
connective tissue. The secretion is therefore rich in cells. 
It also contains comparatively large, round bodies vs^hich 
have the appearance of masses of fat grobules. These 
are the so-called colostrum corpuscles, which are re- 
garded by some as leucocytes which have taken up a large 
number of fat globules, and by others as exfoliated epi- 
thelial cells containing masses of fat globules. A cow 
in this stage of lactation is said to be "fresh." 

During the first week the secretion gradually changes 
to milk. The alveoli of the udder are not all active at 
this time, but those which are inactive and which have 
not undergone permanent involution resume their func- 
tion within the succeeding two or three weeks, when the 
secretion of milk reaches its highest point. Usually by 
the end of the first week the leucocytes have disappeared 
from the alveoli and interalveolar tissue and very few 
cells are present in the milk. But if milking is delayed 
or is incomplete at any time, or if stasis of milk occurs 
from any cause, leucocytes again invade the alveoli and 
interalveolar tissue in large numbers and become nume- 
rous in the milk. Their appearance under these condi- 



PHYSIOLOGY OF MILK SECRETION 5 

tions seems to be for the purpose of preventing stag- 
nation of milk in the alveoli; they take up the fat glo- 
bules in the alveoli and carry them off to the lymph 
stream (Czerny). Leucocytes and exfoliated epithelial 
cells are also present in the milk in large numbers in in- 
flammation of the udder. 

Under natural conditions, the secretion of milk con- 
tinues only until the offspring is able to masticate and 
digest solid food. But in the highly specialized dairy 
cow, in which the function of the udder has been greatly 
developed, lactation may continue for as long as one 
to two years if reimpregnation does not take place, pro- 
vided the milk is regularly withdrawn. When the cow 
is reimpregnated, lactation usually ceases within a few 
weeks of parturition, but in some individuals it continues 
without interruption from one parturition to the next. 
In these latter animals, the secretion changes to colos- 
trum a few days before parturition. Cows in which lac- 
tation is about to cease are called "strippers." Near the 
end of lactation the milk changes very much in composi- 
tion and the cellular content again increases. Quite fre- 
quently it has a salty or bitter taste, or an animal-like 
taste and odor which are unpleasant. It is considered 
good practice to give the udder and the organs of diges- 
tion an opportunity to rest and recuperate before a new 
lactation period begins, and " persistent milkers " are 
frequently "dried off" about a month before the suc- 
ceeding parturition is due. This can usually be accom- 
plished by reducing the feed and gradually stopping 
milking. Periodical emptying of the udder is necessary 
for the continuance of milk secretion, and the opposite 
effect is produced when milking is incomplete or is 
omitted. 



6 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Phases of Milk Secretion. — All of the milk obtained 
from the udder at one milking is not secreted before 
the withdrawal of the milk is begun. The average vol- 
ume of the cavities of the udder is 3,000 c.c, or about 3 
quarts, while the average yield of milk at one milking 
is from 4,000 to 6,000 c.c, or about 4 to 6 quarts (Fleisch- 
mann). A large part of the milk obtained at a milk- 
ing is secreted while the cow is being milked. As much 
milk is secreted in ten to fifteen minutes during milking 
as is formed during the entire period between milkings. 
The secretion of milk may be divided into two phases 
(Zietzschmann) . 

The -first phase occurs during the intervals between 
milkings. Following the completion of a milking, the 
gland remains at rest for a short time until the exhausted 
secretory cells can recuperate ; then secretion is resumed, 
and gradually increases in intensity up to a certain point. 
The udder gradually becomes larger and firmer, but the 
teats remain relaxed and pendulous and contain only a 
small quantity of milk. The greater part of the milk 
secreted during the first phase remains in the alveoli 
and the large milk canals. There are two reasons for 
this : ( 1 ) the horizontal direction of the large milk canals 
does not favor the flow of milk into the cistern, and (2) 
the inward pressure of the erectile tissue in the teat causes 
the mucous membrane to project into the cistern in folds, 
filling up the cavity and opposing the flow of milk into 
it. When the alveoli and the milk ducts and canals be- 
come full, secretion decreases in intensity. Under ordi- 
nary conditions the pressure in the alveoli, ducts, and 
canals does not become sufiicient to overcome the coun- 
terpressure exerted by the erectile tissue in the teats, 



PHYSIOLOGY OF MILK SECRETION 7 

and consequently the milk cistern remains practically 
empty. 

The second phase of milk secretion begins when the 
udder is stimulated reflexly by manipulation of the teats. 
The udder becomes fuller and more tense, the gland sub- 
stance firmer. The teats lengthen and become rigid 
and divergent, while the wrinkles disappear from the 
skin covering them. The udder is distended and the 
cisterns are full of milk. The milk has been "let down." 
All these changes are brought about by the downward 
stroking of the teats, which causes reflexly ( 1 ) dilation 
of the blood vessels and an increased flow of blood to 
the udder, (2) contraction of the walls of the alveoli 
and ducts, which forces the milk down into the cisterns, 
and (3) increased secretion of milk. The same eff'ect 
may be produced reflexly by an irritation of the inter- 
nal genital organs such as may result from irrigation 
of the uterus or vagina, or manual removal of the pla- 
centa, and also by psychic influences like the sight of 
the calf, the clatter of the milk vessels, the sound of milk 
drawn from another cow into a pail, etc. When the 
interval between milkings is too long the milk is "let 
down" spontaneously, but in this case it occurs grad- 
ually. 

As soon as the milk is sufficiently " let down " the 
withdrawal of milk may be begun. The descending pres- 
sure exerted by the hand upon the contents of the milk 
cistern in the operation of milking opens the sphincter 
between the teat canal and the cistern, permitting the 
milk to escape. This pressure operates perpendicularly 
to the wall of the cistern, and when the bottom of the 
cistern is pointed or conical the sphincter is opened more 
readily than when the bottom is flat (see Fig. 4). The 



8 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

manipulation of the teats in milking causes the hyper- 
asmia and increased secretion set up by stroking the teats 
to continue until the secreting cells are exhausted, when 
the flow of milk ceases and the udder becomes smaller 
in size and relaxed. The manipulation of one teat pro- 
duces hypersemia and stimulates secretion in all four 
quarters of the udder. The second phase of milk secre- 
tion is therefore due to the mechanical stimulation result- 
ing from the manipulation of the teats in milking. The 
stimulating apparatus is in the teats, but it is not clear 
how the stimuli -are transmitted. The udder is richly 
supplied with nerves from the sympathetic system and 
from the lumbar plexus, and yet secretion can go on 
after the greater part of the nerve apparatus is discon- 
nected. 

Three factors are concerned in the second phase of 
milk secretion: (1) The vasodilator nerves are stimu- 
lated reflexly by the mechanical manipulation of the 
teats in milking, producing a hypersemia and bringing 
a rich supply of milk-forming material to the secreting 
cells. (2) The operation of milking stimulates also the 
secretory and the motor nerves ; stimulation of the secre- 
tory nerves accelerating the secretory processes in the 
cells of the alveoli, and stimulation of the motor nerves 
causing a contraction of the alveoli and ducts and forcing 
the milk into the cistern. (3) The " milk-formers," which 
circulate in the blood, stimulate the secretory cells 
(Zietzschmann). 

Under certain abnormal conditions the secretion of 
the second phase stops before the usual amount of milk 
is obtained. This may result from fright, sudden anx- 
iety, and in sensitive animals from unusual manipulation 
of the teats (strange milkers) , from sore teats, etc. The 



PHYSIOLOGY OF MILK SECRETION 9 

distended udder is suddenly reduced in size and becomes 
relaxed. This is due to a reflex contraction of the blood 
vessels, which reduces the blood supply, and to the empty- 
ing of the milk cisterns. Contraction of the blood-vessels 
slightly enlarges the alveoli and ducts, creating a va- 
cuum, and the milk in the cisterns is drawn up into the 
alveoli and ducts. It is then said the cow "draws the 
milk up," or "will not give down." In these cases the 
physiological efl'ect of the manipulation of the teats in 
milking is overcome by a stroijger impulse. If these 
impulses are repeated frequently, or are due to more 
or less permanent conditions, like chronic sores on the 
teats, the shortening of the second phase may become 
habitual or permanent. 

The secretion of the first phase is passive and slow. 
According to Zietzschmann, it is due to the stimulant 
effect upon the gland cells of the "milk-formers" cir- 
culating in the blood. 

The secretion of the second phase is active and rapid, 
and is instituted and continued by the manipulation of 
the teats in milking. 

Within certain limits, increasing the number of milk- 
ings, thus shortening the period between milkings, will 
increase the total daily yield of milk. If milked three 
times in twenty-four hours, a cow will usually yield a 
greater total quantity of milk per day than when milked 
twice in twenty-four hours. 

The composition of the milk is different in the first 
and second phases. The first milk drawn from the udder 
at any milking will contain a smaller proportion of 
solids, especially fat, than the succeeding milk. This is 
not due to the fat rising to the top of the fluid in the 
udder, nor to the adhesion of the fat globules to the walls 



10 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

of the alveoli and ducts, as has been suggested, because 
when milk is drawn from the udder at the end of the 
first phase with a milk tube or catheter the composition 
of the first and last milk is about the same; but as soon 
as the teats are manipulated, thus beginning the second 
phase, the per cent, of fat is increased. The milk se- 
creted during the first phase contains a lower per cent, 
of fat than that formed in the second phase. The per 
cent, of other solids is nearly the same in the milk of 
both phases. The original ferments or enzymes, except 
oxydase, are present in greater quantity in milk of the 
second phase than in that of the first. The first milk 
drawn from the udder contains more oxydase than the 
end milk. 



CHAPTER II 

COLOSTRUM 

Beginning a few days before and continuing for sev- 
eral days after parturition, the udder secretes a substance 
called "colostrum," which differs in many respects from 
milk. This fluid is intended for the nourishment of the 
calf during the first days of life outside of the uterus of 
the mother. It contains a very high per cent, of albumi- 
nous compounds in a form in which they can be readily ab- 
sorbed from the digestive tract of the young animal. It 
also contains protective substances from the mother 
(Engel) , which are of value in maintaining health (Im- 
misch), and it has a laxative action upon the bowels of 
the calf, which results in the removal of the meconium. 

Physical Properties. — Colostrum is of a yellowish, 
reddish-yellow, or brownish color; of a thick, slimy, sticky 
or "stringy" consistency, with a peculiar unpleasant odor 
and a salty taste. The yellowish color is due to the pres- 
ence of fat globules, which are frequently clumped to- 
gether, while the reddish or brownish tinge is due to 
the presence of red-blood cells or blood. Containing a 
much greater per cent, of solids than milk, its specific 
gravity is naturally much higher, ranging from 1.040 
to 1.080 and even up to 1.090. 

Chemical Properties. — Albumin and globulin are 

present in colostrum in considerably greater quantity 

than in milk. Nuclein compounds are also to be found 

in larger proportion. There is less casein and sugar, 

about the same per cent, of extractives, but a greater 

proportion of mineral salts. The analysis, as given by 

11 



12 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Eugling, is as follows: Casein 2.65 per cent., albumin 
and globulin 16.55 per cent., sugar 3 per cent., extrac- 
tives 3.54 per cent., ash 1.18 per cent., and water 73.07 
per cent. The high content of albumin and globulin is 
due to the presence of the colostrum bodies and nume- 
rous other cells. The sugar is not lactose, as in milk, 
but glucose, or perhaps a mixture of glucose and galac- 
tose (Tereg). Of the extractives, about 78.2 per cent, 
is fat, 13.8 per cent, cholesterin, and 8 per cent, leci- 
thin. The fat differs from that of milk and is apparently- 
similar to the fat of the tissues. The mineral salts are 
rich in magnesia, to which is attributed the laxative ef- 
fect of colostrum. 

The reaction is acid to litmus. For two to four days 
after parturition the secretion coagulates when boiled 
(see boiling test), on account of the large quantity of 
albumin and globulin present, while it curdles for four 
to twelve days after parturition when mixed with an 
equal volume of 68 per cent, alcohol (see alcohol test). 

Microscopic Appearance. — Viewed under the micro- 
scope, colostrum is seen to contain free fat globules, 
which are not uniform in size like those seen in milk; 
colostrum bodies or corpuscles, which are comparatively 
large, round or mulberry-shaped masses, containing fat 
globules ; leucocytes^ some of which contain fat globules, 
and, in fresh colostrum, show amceboid movement; and 
epithelial cells, which are more or less disintegrated. The 
colostrum bodies are cells which contain large masses of 
fat globules within their protoplasm, but opinions differ 
as to whether they are leucocytes or epithelial cells. 

Ferments or Enzymes.- — Catalase and diastase are 
present in colostrum in greater amount than in milk, but 
at the end of the first week after parturition they are 



COLOSTRUM 13 

reduced to the amount normally found in milk. Oxydase 
and peroxydase may be absent for thirty hours or less 
following parturition, but after that time they are usually 
present (Gruber). 

The bactericidal power of colostrum is greater than 
that of milk. 

Change from Colostrum to Milk. — The secretion of 
the udder changes gradually in appearance and com- 
position until, in about a week after parturition, it be- 
comes milk. According to Weber, the consistency is 
changed to that of milk by the second to the fifth day, 
usually by the third ; the color by the third to the eighth 
day, usually by the fifth, and the reaction by the seventh 
day, although this is variable. The colostrum bodies 
persist for variable periods. In some cows they continue 
to be present indefinitely in small number, while in 
others they are absent even in the first days of secre- 
tion. Shortly before the lactation ceases they again be- 
come numerous. 

Judgment of Colostrum as a Food for Man. — While 
colostrum is of great value to the new-born calf, it is 
not considered desirable as human food. It has not been 
proven to be injurious to the health of man, but the 
odor and taste are obnoxious, and its appearance is unap- 
petizing. Regulations of local health authorities for 
the control of milk supplies, therefore, forbid the sale of 
the product of a cow for food purposes usually for one 
week after parturition, and also for fifteen days before. 
It has been proposed by Weber that the use of the udder 
secretion be prohibited for general food purposes as long 
as it coagulates when boiled (2 to 4 days), and that its 
use for children be forbidden as long as it continues to 
react to the alcohol test (4 to 12 days). 



CHAPTER III 

MILK 

The fluid known as "milk" consists of water and 
certain solids. The latter are in solution, in suspension, 
and in emulsion. In order to comprehend the various 
changes which may occur in milk and to understand the 
different methods for its examination, it is necessary to 
have some knowledge of its physical and chemical prop- 
erties, its microscopic appearance, the ferments or 
enzymes it contains, and the bacteria with which it may 
be contaminated. These points will therefore be given 
consideration. 

CHEMICAL PROPERTIES 

Constituents. — The principal chemical constituents are 
casein, lactalbumin, lactoglobulin, fat, lactose, mineral 
salts, and water. 

Casein is a nucleo-albumin and therefore contains 
phosphorus. It is insoluble in water when free and un- 
combined. But in milk it is combined with calcium in 
the form of dicalcium caseinate. This compound, which 
is neutral to litmus and acid to phenoiphthalein, is re- 
sponsible for the white color of milk, and in part for its 
opacity. It is not in solution in milk, but in suspension. 
When milk is exposed to a low temperature the calcium 
caseinate forms flakes, which, when the temperature is 
sufficiently low, are visible to the eye; it is also more 
readily precipitated. This must be kept in mind when 
the alcohol test is used (page 285). 

If an acid is added to milk the casein is precipitated. 
14 



MILK 15 

The same thing occurs when the lactose in the milk is 
fermented by bacteria and a sufficient quantity of acid 
is produced. The calcium caseinate is split up. The 
acid combines with the calcium, while the free casein, 
being insoluble, is precipitated in the form of a firm, 
jellj^-like white curd. Subsequently this curd contracts 
and expresses a fluid called whey, which contains some 
of the milk fat, the albumin and globulin, the milk sugar, 
the mineral salts, and the calcium salt formed by the 
combination of the acid with the calcium. Most of the 
fat remains in the curd with the casein. This is the com- 
mon sour curdling of milk. If lime water or a dilute 
solution of an alkali is added, the casein will be redis- 
solved and the acidity reduced. 

Rennet or ch}'Tnosin also causes curdling of milk. In 
this case the calcium caseinate is split up by the rennet 
into calcium paracaseinate and a substance known as 
whey-proteid. Calcium paracaseinate, being insoluble, 
is precipitated and forms a cm'd, while the whey-proteid 
is held in solution in the whey. Certain bacteria produce 
a rennet-like ferment, which splits up the casein com- 
pound of milk in the same manner. This is the sweet 
curdling of milk, so called because the milk curdles with- 
out souring. The curd produced in this way cannot 
be redissolved by lime water or a dilute solution of an 
alkali. Curdling of milk may occur from the j oint action 
of acids and the rennet-like ferment. The blood contains 
a ferment, called anti-rennet, which inhibits the action 
of rennet. This ferment is not present in normal milk, 
but when inflammation occurs in the udder and there is 
a transudation of serum from the blood-vessels into the 
udder tissue the anti-rennet ferment is present in the 
udder secretion, which is then not coagulated by rennet 



16 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

at all, or only after several times the usual amount of 
rennet is added. A method based upon these facts has 
been proposed by Sehern for detecting milk from cows 
affected with mastitis, but the test has not come into 
very general use, because it has not been found possible 
to obtain a standardized rennet solution which will not 
deteriorate. 

Fresh milk may be heated to boiling without coagula- 
tion occurring. A thin membrane, which consists prin- 
cipally of casein, forms on the surface, but real coagula- 
tion does not take place. After a certain degree of acid- 
ity has been reached a temperature of 75° C. (167° F.) 
is sufficient to coagulate the casein. 

Casein is formed by the secreting cells of the alveoli 
of the udder from the circulating albumin of the blood 
(Rievel). 

Lactalhumin. — The albumin of milk is in solution. 
It is similar to the albumin of the blood, but differs 
slightly in its chemical composition and polarization. 
It begins to coagulate at 65.6° C. (150° F.), and the 
coagulation increases with the temperature (Rupp). 
Whether the albumin originates from the breaking down 
of cells or is derived from the blood is not known. 

JLactoglohulin. — The globulin of milk originates 
from the disintegration of cells, and is present in milk 
in solution. It coagulates at 75° C. (167° F.) . 

Fat. — The fat is present in milk in an extremely 
finely divided condition — i.e., in an emulsion. Under 
the microscope it can be observed in the form of small 
globules. The specific gravity of the fat is lighter than 
that of any of the other milk constituents, including the 
water, being only 0.93. Consequently the fat globules 
in milk are buoyant, and when the milk is permitted 



MiLi^: 1" 

to stand undisturbed they rise to the top and in a very 
short time form a layer on the top of the fluid, which 
is known as the cream layer or the cream line. By many 
consumers the quality of milk is judged solely by the 
thickness of the cream layer. When the cream is re- 
moved the remaining fluid is called shim milk; or it is 
called separator milk when the cream is removed by a 
centrifugal apparatus known as a separator. 

The fat globules vary in size with the breed, the stage 
of lactation, the feed, at different periods of the same 
milking, and with the individual. In the milk of Jersey 
and Guernsey cows the fat globules are larger than they 
are in the milk of Holsteins and Ayrshires. The cream 
rises more rapidly when the globules are large than when 
they are small. 

Moderately high temperatures also favor the sepa- 
ration of the fat globules from the remainder of the 
milk; therefore when milk is to be run through a sepa- 
rator it is usually warmed to 32° C. (90° F.). On the 
other hand, higher temperatures delay or entirely pre- 
vent the formation of a cream layer. Temperatures 
above 70° C. (158° F.) destroy the cream line entirely. 
A temperature of 65° C. (149° F.) for ten minutes has 
no effect, but as the time of exposure at this tempera- 
ture is increased the formation of the cream layer is 
delayed more and more, until finally, after forty min- 
utes' exposure, it does not form at all. Milk may be 
heated at 63° C. (145.4° F.) for thirty minutes and at 
60° C. (140° F.) for as long as fifty minutes without 
affecting the cream line. The cream does not rise in 
homogenized milk because the fat globules have been 
broken up into fine particles. Such milk is said to be 
more palatable and more digestible than ordinary milk, 
2 



18 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

but these advantages are overbalanced by the expense 
of the process. 

When milk is shaken or agitated the fat globules 
gradually unite and form flakes or lumps — i.e.^ butter. 
Small clumps of butter fat may form in milk during 
transportation when the container is not full. This 
change may affect the test for fat. If milk or cream 
is slightly acid and warm, the clumping of the fat glo- 
bules is facilitated. Hence cream is usually churned 
after it has attained an acidity 0.4 per cent., and at a 
temperature of 21° C. (70° F.). Cream from a cow 
near the end of lactation may not "butter" because of 
its alkalinity. 

The fat of milk differs in its chemical and physical 
properties from both the fat of the tissues and the fat 
of the food. It consists of a mixture of fats, princi- 
pally olein, stearin, and palmatin, together with some 
butyrin and other fats. Its composition varies, being 
influenced by the breed, feed, external conditions, etc. 
Cotton-seed meal, for example, increases the olein and 
raises the melting point. When milk fat decomposes, 
butyric acid is liberated and produces a rancid odor and 
taste. The color of the milk fat is more or less yellow. 
The fat globules, by reflecting the light, are partly re- 
sponsible for the opacity of milk. 

In regard to the origin of the milk fat, it appears 
most probable that it is derived in part from the splitting 
up of albuminous compounds in the udder or in another 
part of the body, or in both places. It may also be formed 
from the carbohydrates which are carried to the udder 
by the blood (Rievel). 

Lactose. — This substance, also known as "milk 
sugar," is in solution in milk. It is a disaccharid and 



MILK 19 

may undergo different varieties of fermentation when 
acted on by microorganisms. Certain bacteria split up 
lactose into lactic acid and certain by-products (carbon 
dioxide, hydrogen, formic acid, butyric acid, etc. ) . These 
organisms are the cause of the common "souring" and 
curdling of milk. The bacteria of the coli-aerogenes 
group ferment lactose and form acids and gases (lactic, 
acetic, and succinic acids, carbon dioxide, carburetted 
hydrogen, oxygen, and nitrogen) . 

Under normal conditions, lactose is found only in 
the milk. If milk is retained in the udder from any 
cause, as incomplete milking, omission of milking, udder 
disease, etc., then lactose appears in the urine. When a 
secreting udder is completely extirpated, glucose is tem- 
porarily present in excess in the blood and appears in 
the urine, while lactose appears in the urine if the udder 
tissue is not completely removed. These latter facts are 
taken to indicate that milk sugar is formed in the udder 
from the glucose carried to it by the blood. 

Salts. — The salts of milk, which are in solution, are 
very largely inorganic. Calcium, potassium, and sodium, 
together with small quantities of magnesia and oxide 
of iron, are present in combination with phosphoric acid, 
sulphuric acid, chlorine, and carbonic acid. A small por- 
tion of the basic substances is in combination with citric 
acid and probably with other organic acids. 

Water. — The water of milk is derived from the blood. 
The milk constituents, except the water, are referred 
to as the milk solids, total solids, or dry matter. The 
casein, albumin, globulin, lactose, and salts are desig- 
nated as solids not fat. 

Variations in Composition. — While normal milk always 
contains the same chemical constituents, the proportions 



20 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

in which they are present vary very much. The fat shows 
a greater variation than the other sohds. In milk rich 
in total solids, the fat content is frequently considerably 
above the average, while the per cent, of solids not fat 
only slightly exceeds the average. On the other hand, 
in thin, poor milk the fat per cent, may be far below 
the average, while the per cent, of solids not fat is not 
very far from the average. Milk from individual cows 
shows a greater variation in composition than different 
samples of market milk, which is a mixture of the milk 
from a number of cows. 

Individual milk may show the following variations 
in the proportion of the different constituents: fat, 2.5 
to 7.5 per cent. ; lactose, 4 to 5.8 per cent. ; casein, 2 to 5 
per cent.; albumin, 0.39 to 0.95 per cent.; globulin, a 
trace; salts, 0.35 to 1.21 per cent.; water, 83 to 89 per 
cent. 

The fat content shows the greatest range of varia- 
tion and the lactose the least. These variations must be 
taken into consideration in collecting samples of milk 
for certain tests and in judging the results of tests for 
adulteration and skimming. They are due to a number 
of causes. 

Some of these causes, such as the breed, individuality, 
and stage of lactation, are more or less regular and con- 
stant in their operation. As a rule, cows of the Jersey 
and Guernsey breeds give milk richer in fat than Hol- 
steins and Ayrshires, but some individuals of the Hol- 
stein and Ayrshire breeds give milk with a higher fat 
content than some Jerseys and Guernseys. Early in the 
stage of lactation, when the milk flow is most abundant, 
the proportion of solids, especially the fat, is less than it 
is later, when the milk flow has decreased. Instances 



MILK 21 

are kno^vn where the addition of several "fresh" cows 
to a small herd at the same time has reduced the fat per 
cent, of the mixed milk below the standard formerly- 
maintained. In the last month of lactation, when the 
secretion decreases rapidly, the proportion of solids 
usually increases, especially the fat. At the same time, 
the secretion reacts decidedly alkaline to litmus paper 
and usually has a salty taste ; sometimes it has an animal- 
like odor and taste. Cows in this stage of lactation are 
called "strippers." In exceptional cases the milk does 
not show any noticeable change in chemical composition 
during the entire period of lactation, while in rare cases 
the per cent, of solids may decrease at the end of lacta- 
tion. At dijferent stages of the same milking the milk 
also shows a regular and constant variation in composi- 
tion, the first milk drawn containing a lower per cent, 
of fat than the last or "end" milk. Incomplete milking 
may lower the per cent, of fat, because the end milk is 
much richer in fat than the first milk. 

Transitory and irregular variations in composition 
may be observed in the milk of the same cow from day 
to day, or even in the milk drawn at different milkings 
on the same day. The fat content may show a difference 
of as much as one per cent. These variations are attrib- 
uted to change in the character of the feed, or in the time 
of feeding and watering, change of milkers, the weather, 
change of stable, and unusual occurrences ( storms, stran- 
gers, etc. ) . The quantity of milk secreted is also affected 
by the same causes. While the feed has no pronounced 
permanent effect on the composition of the milk, a change 
from dry to green feed may cause a temporary increase 
in the fat of from 0.5 to 1 per cent., while distillery slops 



22 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

or other very watery feed may cause a temporary de- 
crease of from 0.25 to 0.5 per cent. 

The time of milking will influence the composition of 
milk. When the intervals between the milkings are 
equal and the feed, amount of water, etc., are the same, 
there is no difference between the composition of the 
morning and evening milk; but in practice the periods 
are usually unequal, i.he shorter interval preceding the 
morning milking in the summer and the evening milking 
in winter. At the milking following the shorter interval 
the quantity of milk obtained is less and the fat per 
cent, is greater than at the other milking. Hence it fol- 
lows that in summer the morning's milk is richer in fat 
but of lesser quantity than the evening's milk, while in 
winter the reverse is true. The age of the cow has no 
appreciable effect on the composition of milk. Volun- 
tary exercise in the open air increases the fat per cent, 
as well as the quantity of milk yielded; forced exercise 
decreases the water in the milk and consequently de- 
creases the volume of the milk flow, but the per cent, of 
fat is increased, while violent exercise reduces both the 
volume and the per cent, of solids. The effects of oestrum 
are not uniform ; the fat may be increased or decreased, 
the albumin may be increased to such an extent that the 
milk will curdle when boiled, or there may be no change 
in the composition. In one test of milk from a cow with 
nympJiomania the proteids were increased to 5.72 per 
cent. Weaning, or removing the calf, when it causes the 
cow to become restless and fretful, is attended with a 
decrease in the fat per cent. The variations in quantity 
and composition caused by disease will be considered in 
the chapter on the " Influence of Disease on Milk." 

Market Milk varies less in composition than indi- 



MILK 23 

vidual milk, because the different variations in the milk 
of individual cows balance one another more or less. 
Under certain conditions, milk from different herds, i.e,, 
herd milk, may show a greater variation in composition 
than the mixed milk of several herds. For example, milk 
from a Jersey or Guernsey herd will usually show a 
higher fat content than milk from a Holstein or Ayr- 
shire herd. The presence of a large proportion of "fresh" 
cows in a herd at one time may cause the mixed milk 
of the herd to be low in solids, especially fat, while a 
large proportion of "strippers" may have the opposite 
effect. The per cent, of fat in market milk may range 
from 3 to 5 per cent., and the per cent, of solids not 
fat from 8.5 to 10.5 per cent. The average composition, 
as reported by Flieschmann, is : fat, 3.4 per cent. ; lactose, 
4.6 per cent.; casein, 3 per cent.; albumin, 0.5 per cent.; 
globulin, a trace; salts, 0.75 per cent.; water, 87.75 per 
cent. 

Over 5000 samples of milk examined at the New 
York State Experiment Station at Geneva, N. Y., were 
found to contain an average of 3.9 per cent, of fat, 
5.1 per cent, of lactose, 2.5 per cent, of casein, 0.7 per 
cent, of albumin, 0.7 per cent, of salts, and 87.1 per cent, 
of water. 

Although it is unusual, normal market milk may fall 
below the usual limit for solids, especially fat, particu- 
larly milk from a single herd, under some of the condi- 
tions mentioned above. For this reason, difficulty has 
at times been experienced in legally proving that milk 
has been skimmed or diluted with skimmed milk or water, 
and this has led to the adoption of legal standards for 
milk and other dairy products by different states, the 
United States government, and some municipalities. 



24 



PRINCIPLES AND PRACTICE OF MILK HYGIENE 





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26 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

The standard of the United States Department of 
Agriculture calls for 3.25 per cent, of fat and 8.5 per 
cent, solids not fat for milk; 9.25 per cent, solids for skim 
milk, and 18 per cent, fat for cream. The standards for 
milk and other dairy products adopted by the various 
states and territories, as reported by the United States 
Bureau of Animal Industry, will be found on pages 
24 and 25. 

Reaction. — The reaction of milk is amphoteric to lit- 
mus — i.e., it turns blue litmus red ( acid monobasic phos- 
phates) and changes red litmus to blue (alkaline di- 
basic phosphates). To phenolphthalein solution it is 
acid. When phenolphthalein solution is added to milk, 
no color reaction occurs, because the color of phenol- 
phthalein solution is not changed by acids. But if, after 
the addition of phenolphthalein solution, sodium hydrox- 
ide solution is added to the milk in excess of the amount 
necessary to neutralize the acidity the fluid assumes a 
pink color, which is permanent. This reaction is made 
use of in determining the degree of acidity of milk and 
cream. 

To neutralize the acidity in 100 c.c. of normal, fresh 
market milk, 18 to 19 c.c. of a one-tenth normal solution 
of sodium hydroxide are required. This represents an 
acidity of 0.16 to 0.17 per cent. The acidity of milk 
when it is drawn from the udder is less than 0.1 per cent. 
This original or native acidity is due to the casein and 
acid phosphates. The fermentation of the milk sugar 
by bacteria increases the acidity. Lactic or other acids 
formed in this manner are present whenever the acidity 
is over 0.1 per cent. Market milk with an acidity of 0.1 
to 0.2 per cent, is considered fresh and good. In some 



MILK 27 

cities the legal limit is 0.2 per cent. A sour taste is not 
present until the acidity exceeds 0.3 per cent. 

The acidity of colostrum is about three times as great 
as that of milk. As the colostrum changes to milk, the 
acidity gradually decreases until it reaches the point 
noraial for milk. Toward the end of lactation the acidity 
is further decreased, and in "strippers" is very low, or 
the reaction may even be alkaline. 

The reaction of the milk of individual cows is usually 
below normal in acidity, or may even be alkaline, in ordi- 
nary inflammations of the udder, tuberculosis of the 
udder, and probably also when the udder is eliminating 
abnormal substances, as in cowpox; but this is by no 
means always the case. In streptococcic mastitis the 
milk may be more acid than normal. The reaction alone 
of the milk of individual cows cannot therefore be relied 
upon to discover diseased conditions. It is hardly neces- 
sary to mention that nothing can be learned on this point 
from determining the reaction of market milk. 

High acidity in market milk is usually the result of 
excessive fermentation of the lactose, and is an indication 
that the milk is stale, or was produced under unclean 
conditions, or was not properly cooled and cared for. 
The addition of boric acid or formaldehyde also increases 
the acidity. Salicylic acid has less effect on the reac- 
tion because it is usually not added in very great quan- 
tity. The acidity may be reduced by the addition of alka- 
lies (bicarbonate of soda, chalk, potash) , but the addition 
of these substances to milk is illegal. Addition of water 
and heating (loss of CO2) also reduce the acidity. 

(For methods of determining acidity, see pages 254 
to 257.) 



28 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

PHYSICAL PROPERTIES 

The physical properties of milk which are of great- 
est importance in milk hygiene are the color, odor and 
taste, specific gravity, and refraction. Other physical 
properties which have been extensively studied are the 
viscosity, surface tension, freezing point, and electrical 
conductivity. 

Color. — Milk is a white, opaque fluid, sometimes with 
a yellowish or bluish tinge. The white color is due to 
the calcium caseinate, while the opacity is due in part to 
the same substance and in part to the fat. Not only the 
quantity of fat, but also the size of the fat globules, 
aif ects the opacity, the opacity being less when the glo- 
bules are large than when they are small. Since opacity 
does not depend entirely on the quantity of fat, tests for 
fat based upon transparency, such as the lactoscope test 
(p. 239), are not accurate. The yellowish tinge of milk 
is due to a pigment in the fat (carotin) ; it is more pro- 
nounced in milk from cows of certain breeds, as the 
Guernseys. A bluish tinge indicates that the milk has 
a low fat per cent., and is sometimes associated with skim- 
ming and watering, but it must be remembered that any 
milk in a thin layer has a bluish tinge. 

Odor and Taste. — N^ormal milk has a slight odor, 
resembling the exhalations from the cow's skin, and a 
slightly sweetish taste. During the colostral period and 
near the end of lactation, individual cow's milk may have 
a salty, hitter j, or a rancid, animal-like taste. A large 
proportion of "strippers" in a herd may give the mixed 
milk a similar taste. The milk of the individual cow may 
also be salty or bitter in advanced pregnancy, after abor- 
tion, in mastitis, and when digestion is disturbed. Milk 
with a certain degree of acidity will acquire a hitter. 



MILK 29 

astringent taste in rusted vessels in consequence of the 
formation of iron lactate. A "jishy'^ taste may also be 
present when the milk vessels are rusty or when they 
have not been rinsed free of soap powder. 

Certain aromatic feeds impart a characteristic odor 
and taste to the milk. Among these are ensilage, rape, 
cabbage, and beets, turnips, rutabagas, carrots, and their 
tops. This is not ordinarily due to the ingestion with the 
feed of substances responsible for the taste and odor and 
their elimination with the milk through the udder, but 
to the absorption by the milk of the odor of the feed from 
the air of the stable. This is demonstrated by the fact 
that when these feeds are fed in ordinary quantity and 
after milking, and not unmediately before or during 
milking, the odor and taste of the milk are not affected. 
If these feeds are given in large quantity, it is probable 
that some of the aromatic substances may be excreted 
through the udder. In the case of garlic, however, the 
volatile oil to which the odor of that substance is due is 
eliminated through the udder in the milk. Odors are 
readily absorbed by milk, especially when it is warm. 
Milk drawn and allowed to stand in an unclean or poorly 
ventilated stable will acquire a stable-like odor and taste. 
It has been demonstrated experimentally that if milk 
at a temperature of 14 to 22° C. (57 to 72° F.) is ex- 
posed to the odor of ensilage or horse manure for a half 
hour to an hour and a half it will acquire an odor and 
taste resembling these substances (Russell). 

Abnormal odors and tastes result also from the 
growth of bacteria in milk. The activity of the pepton- 
izing bacteria may produce first a bitter taste, due to 
the production of peptone, and later a foul and unpleas- 
ant odor and taste, the result of decomposition processes. 



30 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Bacilli of the coli-aerogenous group may produce an 
unclean^ even nauseating, taste with a stable or manure- 
like odor, while the lactic acid bacteria give to milk a 
sour odor and taste. Specific organisms have been iden- 
tified which produce hitter, soapy, oily, and burnt tastes 
and a stable-like odor and taste. Other bacteria produce 
a rancid odor and taste, and some produce an unclean 
odor and taste. Wliile some of the peptonizing bacteria 
(udder cocci) are normal inhabitants of the udder, the 
other bacteria usually enter the milk after it is drawn 
from the cow. Sometimes, however, bacteria which are 
the cause of abnormal odors and tastes become estab- 
lished in the udder. Odors and tastes of bacterial origin 
are often not apparent until a certain period after the 
milk has been taken from the udder and usually become 
more pronounced as the milk increases in age. Milk 
acquires a cooked taste when heated above 68 to 71° C. 
(155 to 160° F.) Heating in open vessels has a more 
pronounced effect on the taste than heating in closed 
vessels or bottles. 

The senses of smell and taste tire very quickly and 
cannot be depended upon to judge many samples of 
milk. Odors and tastes are more apparent when the 
milk is warm. 

Specific Gravity. — As would naturally be expected 
from the statements made in regard to the variation in 
the composition of milk, the specific gravity or density 
of different samples of milk varies considerable. The 
range of variation is greater for individual milk than 
for market milk. The specific gravity of the milk of 
individual cows will range from 1.027 to 1.040, while 
that of market milk will fluctuate between 1.028 and 
1.034, with an average of 1.032, at the standard tempera- 



MILK 31 

ture of 15° C. (60° F.). At higher temperatures the 
specific gravity or density is decreased, and at lower tem- 
peratures it is increased. 

The specific gravity depends not only upon the total 
quantity of solids contained in the milk, but also upon the 
relative proportion in which the individual solids are 
present, because the individual solids are of different spe- 
cific gravity. Fat shows the greatest difference, being 
much lighter than the other solids ; it is even lighter than 
water. The solids not fat are all heavier than water, 
the specific gravity of the salts being 4.12, lactose 1.666, 
and proteids 1.346 (Richmond) . Therefore the removal 
of fat, i.e. J, skimming, increases the specific gravity, and 
the addition of skim milk has the same effect, while the 
addition of water reduces the specific gravity. But the 
specific gravity has such a wide normal variation that 
it is possible to remove a small amount of fat from milk 
with a normally low specific gravity without causing the 
specific gravity to rise above the normal range, and, 
conversely, a certain amount of water may be added to 
milk with a normally high specific gravity without lower- 
ing the specific gravity below the normal Hmit. How- 
ever, in the first case the per cent, of fat will be decreased, 
and in the second there will be a decrease in both the per 
cent, of fat and of solids not fat. When the specific 
gravity of milk is raised above the normal by skimming 
it may be brought within the normal range by the addi- 
tion of water, but the per cent, of fat and of solids not 
fat will be decreased. Therefore, in examining market 
milk to detect skimming or the addition of skimmed 
milk or water, the per cent, of fat and of solids not fat 
must always be considered in connection with the spe- 
cific gravity. (For method of determining the specific 



32 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

gravity, see page 228.) Determination of the specific 
gravity of the milk solids and of the per cent, of fat 
in the milk solids will assist in detecting milk which has 
been skimmed or skinuxied and watered. ( See page 246 
for methods.) The milk solids of normal market milk 
have a specific gravity of 1.31 to 1.36, and the per cent, 
of fat in the milk solids is 20 to 34. When milk is 
skiimned or skimmed and watered, the specific gravity 
of the milk solids is increased, while the per cent, of fat in 
the solids is decreased. 

The influence of disease on the specific gravity of 
individual milk is not constant, but the specific gravity 
is usually lowered. However, the specific gravity of 
individual cow's milk cannot be made use of to discover 
diseased conditions, because milk from different cows 
shows such great variations under normal conditions. 
The specific gravity of milk is lower when it is drawn 
from the udder than it is several hours later. 

Refraction. — Kays of light passing through one me- 
dium into another of different optical density, as through 
air into milk, are broken or refracted at the point of con- 
tact of the two media. The degree of refraction, or the 
refractive power compared with that of air, is called 
the refractive index. Since the calcium caseinate and 
fat contained in milk prevent the light rays from passing 
through it, these substances must be removed before the 
refractive index can be deteiTnined. The refractive index 
of milk, so-called, is really the refractive index of the 
milk sei-um or whey, i.e., the milk minus the calcium 
caseinate and fat. 

The refractive power of the milk serum depends upon 
the quantity of lactose or of lactose and salts present. 
Adding water to milk reduces the proportion of these 



MILK 33 

substances, and therefore reduces the refractive index. 
Hence the refractive index may be used to detect watered 
milk. (See method on page 249.) The refractive index 
of normal market milk ranges from 1.3429 to 1.3445. 
On the scale of the Zeiss dipping refractometer, the 
reading for normal milk ranges from 37.3 to 41.5. 

Viscosity is manifested by the adherence of milk to 
the sides of a glass vessel. It increases as the tempera- 
ture of the milk is lowered, and vice versa. It is de- 
creased by skimming and by the addition of water. Dur- 
ing the colostral period and near the end of lactation it 
is greater than at other times during the lactation period ; 
it is also increased in disease or injuries of the genital 
organs, especially the udder. 

Boiling momentarily, or heating for a longer time 
at lower temperatures, decreases the viscosity of milk, 
causing it to appear thinner than normal raw milk. 
Cream heated at 60° C. (140° F.) for twenty minutes 
appears thinner and less viscous than raw cream with 
the same fat per cent, and will not "whip" readily. Vis- 
cogen, a mixture of cane sugar and lime, has been added 
to heated cream to overcome this change. This prepara- 
tion has also been used to increase the viscosity of raw 
cream of low fat per cent., and also to increase the con- 
sistency of skimmed or watered milk. The addition of 
viscogen to cream or milk is illegal unless the product is 
sold as visco-cream or visco-milk. The specific gi'a\aty 
of watered or skimmed milk is increased by the addition 
of viscogen, and the per cent, of solids not fat, especially 
the salts, is also increased. The acidity is reduced. 

Starch is also added to cream to increase the body 
or consistency. 

Freezing Point. — The freezing point of milk is 



34 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

—0.54 to —0.57° C. (31.02 to 30.9° F.) . It varies with 
the amount of the dissolved substances contained in the 
milk, especially the salts. When water is added to milk 
the freezing point rises, while in disease it is sometimes 
lowered and sometimes raised. The determination of 
the freezing point has as yet proven of no practical value 
in routine milk examination. Surface tension and elec- 
trical conductivity are likewise of no practical impor- 
tance. 

MICROSCOPICAL APPEARANCE OF MILK AND MILK SEDIMENT 

When examined under the microscope, milk is found 
to contain numerous fat globules with a few cells, cell 
fragments, and free nuclei scattered among them. If 
a small quantity of milk is placed in a sediment tube and 
centrifugalized, only a part of the cells and cell remnants 
are thrown down to the bottom of the tube with the 
heavier constituents of the milk; many adhere to the 
fat globules and are carried to the top, while the others 
remain in the intermediate fluid. According to Prescott 
and Breed, only about one-fourth is contained in the 
sediment, one-half being in the cream and the remainder 
in the milk. Heating the milk to 60° C. (140° F.) or 
above before centrifugalizing will increase the cellular 
content of the sediment. If some of the sediment is 
spread out in a thin layer on a glass slide, dried in the 
air, fixed by heating, and stained, the cellular bodies can 
be more readily studied. 

Cellular Content. — It will then be observed that the 
cells are of two principal kinds: leucocytes and epithe- 
lial cells. The leucocytes are of the polymorphonuclear 
and lymphocyte varieties, while the epithelial cells are 
of the pavement, cuboidal and cylindrical types. Fre- 



MILK 35 

quently the epithelial cells are folded on themselves, when 
they appear as rounded, oval, or irregular shapes, and 
sometimes they are arranged in groups like the petals of 
a flower. Degenerated and disintegrated cells, free nu- 
clei, bacteria, and vegetable cells and fibres may also 
be present. 

Number of Cells. — The number of cells in different 
samples of milk will vary very much. Milk from indi- 
vidual cows in normal condition may contain from 50,000 
to 1,000,000 and over per c.c. (Savage). Milk from 
the same cow may show considerable differences when 
examined at intervals of a week or a month, and varia- 
tions may also be found in the milk from different quar- 
ters of the udder of the same cow. The number of cells 
may differ at different stages of the same milking, being 
much greater in the end milk than in the first milk. 

The cellular content is very high for a few days after 
calving. Near the end of lactation the cells again in- 
crease in number, and they are also present in excess 
after incomplete or delayed milking. In mastitis there 
is usually a pronounced increase in the number of cells, 
particularly the leucocytes. In some cases the number 
is as high as 200,000,000 to 300,000,000 per c.c. ( Sav- 
age), but in others it is as low as 500,000 per c.c. The 
cell content of milk from an udder affected with mastitis 
exhibits two other featiu*es which are important, viz: 
the cells are clumped or grouped together, and 75 to 80 
per cent, are polymorphonuclear leucocytes. Red-blood 
cells may also be present in the milk when the udder is 
very much congested, as may occur at the beginning of 
lactation and in acute inflammation, and also following 
traumatic injuries. 

The differences in the cell content of the individual 



36 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

milk of normal cows are likely to balance one another 
when the milk of several cows is mixed together; con- 
sequently different samples of market milk show less 
variation in the number of leucocytes than individual 
milk. On the other hand, when the milk from one cow 
affected with mastitis is mixed with the milk of other 
cows in the herd which are in normal condition, the cell 
content of the mixed milk is not likely to be very much 
increased unless the herd is a very small one or the milk 
from the diseased cow contains an enormous number of 
cells. 

Several methods have been devised for detecting an 
excessive number of cells in milk (see pages 281 to 284) . 
When used to examine the milk of individual cows, 
these methods are of great assistance in discovering cases 
of mastitis before clinical symptoms or visible milk 
changes appear, but when applied to samples of mixed 
market milk they cannot be depended upon entirely for 
the purpose of detecting mastitis in the herds supplying 
the milk. 

BIOLOGICAL PROPERTIES OF MILK 

Fennents or Enzymes. — Milk contains a number of 
ferments or enzymes. Some of them resemble the di- 
gestive ferments in their action. This class includes a 
proteolytic ferment called galactase, and diastase, an 
amyloljrtic ferment. These ferments are believed to 
assist in the digestion of milk. A tripsin-like ferment 
and fat-splitting ferments or lipases have been reported, 
but their existence is questioned. There are also oxidiz- 
ing ferments : the oxydases and peroxydase, and reduc- 
ing ferments: catalase and reductase. The diastase. 



MILK 37 

peroxydase, catalase, and reductase reactions have been 
made use of in milk control work. 

Original and Bacterial Ferments. — In milk hygiene 
it is important to distinguish between original and bac- 
terial ferments. An original ferment is one which is 
secreted by the cells of the udder, or which is contained 
in cells like the leucocytes and becomes free in the milk 
when these cells disintegrate. A bacterial ferment is 
secreted by the bacteria which gain access to milk after 
it is formed in the udder. A bacterial ferment increases 
in quantity after milk is drawn from the udder as a result 
of the growth of bacteria, and if it is destroyed by heat 
it will again appear unless the bacteria are all killed and 
the milk is not reinfected. On the other hand, an original 
ferment cannot increase in quantity after the milk leaves 
the udder, and if it is destroyed by heat it does not reap- 
pear in the milk. Diastase and peroxydase are original 
ferments, catalase is both an original and a bacterial 
ferment, and reductase is a bacterial ferment. 

Diastase. — One hundred c.c. of normal milk will di- 
gest 0.015 to 0.02 gramme of starch in thirty minutes. 
This action is due to an amylolytic ferment contained in 
the milk, which has been called diastase. This ferment 
operates best at a temperature of 45° C. (113° F.) and 
is destroyed by a temperature of 65 to 68° C. (149 to 
154° F.) for thirty minutes. It is present in the milk 
when it is formed in the udder, and is therefore an orig- 
inal ferment. It is not produced by bacteria. Colostrum 
is richer in diastase than ordinary milk, and the ferment 
is also present in greater quantity near the end of lac- 
tation. The end milk contains more diastase than the 
first milk drawn from the udder. ( See diastase test on 
page 297. ) 



38 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Per oxydase. — If paraphenyldiamin or tincture of 
guaiac is added to milk with a little hydrogen peroxide, 
the milk at once assumes a blue color. This change 
occurs because the ferment contained in the milk called 
" peroxydase " splits off oxygen from the hydrogen 
peroxide and this free oxygen oxidizes the paraphenyl- 
diamin or the guaiac to a colored compound. If the milk 
is heated to 80° C. (176° F) , the reaction does not occur 
because the ferment is destroyed. The reaction occurs 
best at 40 to 50° C. (104 to 122° F.). Peroxydase is 
present in milk when it is formed in the udder and it is 
not secreted by bacteria. It is therefore an original 
ferment. (See tests for heated milk on page 298.) 

Catalase. — This ferment, which is also known as 
superoxidase, possesses the specific property of splitting 
up hydrogen peroxide into water and oxygen. The re- 
action which occurs is as follows : 2H2O2 = 2H2O + O2. 
Catalase is both an original and a bacterial ferment. It 
is secreted with the milk and is contained in leucocytes 
and in blood. It is also secreted by many of the bacteria 
found in milk, but the various species differ in their 
capacity to produce the ferment. The putrefactive or- 
ganisms appear to produce it in the greatest quantity. 
The ability of the lactic acid bacteria to produce catalase 
is in dispute. 

The amount of catalase in milk as it comes from the 
udder varies at different stages of lactation. The cata- 
lase content is high during the colostral period and this 
condition usually continues for three weeks, although in 
exceptional cases it falls to the amount normal for milk 
by the fourth or fifth day after parturition. ISTear the 
end of lactation, when the milk has fallen to about a 
quart per day or less, the catalase again increases. Some 



MILK 39 

observers report that no increase occurs duing oestum, 
but others state that when the cow is nervous and excitable 
the catalase is sometimes increased. Pronounced changes 
in the feed may affect the quantity of catalase. The 
first milk drawn at a milking contains less catalase than 
the end milk. 

When milk is separated, the greater portion of the 
catalase passes over into the cream. Skim milk, there- 
fore, has a very low catalase content. After milk has 
reached a certain degree of acidity (about 0.36 per cent.) , 
the acid begins to exert an inhibitory influence on the 
activity of the catalase. Up to this point the catalytic 
activity is increased because the amount of catalase is 
increased by bacterial growth. In milk which has under- 
gone " sour curdling," the catalase is paralyzed by the 
acid and is inactive. The catalytic activity may be re- 
stored to such milk by neutralizing it with lime water. 

When milk is exposed to a low temperature in winter 
or to prolonged refrigeration, the catalase is partially or 
completely destroyed. Catalase operates best at a tem- 
perature of 37° C. (98.6° F.) . The lethal temperature is 
around 68° C. (154° F.), but varies within wide limits 
according to the source of the catalase. Heated milk 
may be reactivated, since catalase is a bacterial as well 
as an original ferment. ( See catalase test on pages 287 
to 294.) 

Reductase. — If a small quantity of methylene blue 
solution is added to milk, the mixture will be colored 
blue, but the blue color will disappear after a time because 
the methylene blue is reduced and converted into its 
leuco-base. This change is brought about by a ferment 
in the milk called reductase. If formalin is added to the 
methylene blue solution, forming what is known as Schar- 



40 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

dinger's reagent, and a little of this solution is added to 
milk, the mixture will also be colored blue, but the color 
will disappear more rapidly. At first the difference in 
the time of reduction was attributed to the difference in 
the composition of the solution, but further research 
demonstrated the presence in milk of two different re- 
ducing agents. The ferment which reduces the methylene 
blue solution is called " M-reductase," while the one 
which reduces the formalin-methylene blue solution has 
been named " FM-reductase." 

M-Reductase, — This ferment is not secreted in the 
udder with the milk. It is generally regarded as of 
bacterial origin, although the opinion has been expressed 
(Burri and Kiirsteiner) that the cellular elements of 
milk, like all living protoplasm, have a reduction power 
and that the high reduction power of colostrum during 
the first day after parturition and of mastitis milk is due 
to the rich cellular content of these secretions. It has 
been well established, however, that the capacity of milk 
to reduce methylene blue increases with the number of 
bacteria. 

The different species of bacteria vary in their reduc- 
tion power. Reduction power appears to depend first 
upon the species, then upon the number of bacteria, and, 
finally, upon the media in which the organisms are grow- 
ing. The anaerobic organisms usually have a greater 
reduction power than the aerobes, while the facultative 
anaerobes act more powerfully in the absence of oxygen 
than when it is present. The colon bacilli belong to the 
facultative anaerobes of high reduction power. On the 
other hand, the reduction power of the lactic acid bacteria 
is weak. Different samples of fresh milk containing 
about the same number of bacteria may differ greatly in 



MILK 41 

reduction power because of the difference in the species 
of bacteria present. But, according to Barthel and O. 
Jensen, when milk is stored under suitable conditions, 
the relative proportion of the different species of bac- 
teria present is almost always changed in favor of the 
lactic acid organisms, so that in the case of market milk 
there is usually correspondence between the reduction 
time and the number of bacteria. 

The reduction power of a microorganism is not con- 
stant, but depends upon the vitality of the organism; it 
will therefore decrease with the age of the organism and 
also when nutritive conditions are unfavorable. Hence, 
the reduction activity of milk rich in bacteria is relatively 
less than milk containing fewer bacteria. These factors 
render the reductase test less exact than the plate method 
for estimating the number of bacteria in market milk, 
but not for judging the " keeping qualities " of the 
milk, since the more vitally active the contained bacteria 
the more rapidly will the milk undergo bacterial decom- 
position. 

The reduction power of cream is greater than that 
of skim milk. The reduction power is greatest just be- 
fore curdling. In curdling, the ferment is precipitated 
with the curd. The ferment operates best at a tem- 
perature of 40 to 55° C. (104 to 131° F.) and is 
destroyed by a temperature of 70 to 80° C. (158 to 
176° F.). 

FM-Reductase. — The knowledge concerning this 
ferment is not sufficiently definite at this time to be of any 
value in the practice of milk hygiene. FM-reductase 
is present in colostrum on the first day after parturition 
and is then absent from the udder secretion for two to 
three weeks, when it again appears in the milk. Schern 



42 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

therefore proposed the FM-reductase test as a means of 
determining whether or not a cow is " fresh." FM- 
reductase is absent, or present only in very small quan- 
tity, in the first milk drawn at a milking, but it is always 
present in the end milk. After stasis of milk, it is absent. 
The reaction cannot be used for the detection of mastitis, 
because while reduction occurs rapidly in some cases, in 
others it occurs more slowly than in normal milk or may 
not occur at all. 

Antibodies or Immune Bodies. — Antibodies are sub- 
stances which are produced in the animal body to pro- 
tect it from the action of bacteria or their toxins. The 
term includes antitoxins, agglutinins, precipitins, op- 
sonins, lysins (amboceptors), complement, etc. Comple- 
ment is always present in the blood and the other kinds 
of antibodies are also contained in the normal serum in 
a non-specific form, but these antibodies do not appear in 
the blood in a specific form until after the body is invaded 
by pathogenic organisms or their toxins. 

It has been demonstrated that antitoxins, agglutinins, 
and opsonins pass over from the blood into the milk when 
the udder is in a normal condition. Bacterio-lysins are 
eliminated in the milk when the udder is affected with 
mastitis and during the colostral stage, but it is doubtful 
if they pass over from the blood into the milk under nor- 
mal conditions at other times. Complement is present 
in colostrum and also in milk when the udder is affected 
with mastitis. It may be present in normal milk for as 
long as twenty-six days after parturition, but after that 
time it is absent, according to some observers. The com- 
plement demonstration test has not come into general 
use for the detection of mastitis principally because cer- 



MILK 43 

tain investigators have reported that complement is 
always present in milk from apparently normal cows. 

The quantity of antibodies in the milk compared with 
the quantity circulating in the blood is not definitely 
known. The question has been more extensively studied 
in connection with antitoxins than with the other anti- 
bodies, and it was found that the milk contains only one- 
thirtieth to one-fifteenth of the quantity of antitoxin 
circulating in the blood. Agglutinins may be present 
in the milk in the same quantity as in the blood, or in 
greater or less amount. The immunizing value of the 
milk has not been completely determined. It has been 
demonstrated that antibodies in milk ingested by suck- 
lings are absorbed through the intestines into the blood 
when the suckling and the animal from which the milk 
is obtained are of the same species. There is no direct 
evidence, however, that the antibodies are absorbed into 
the blood of the young animal when the milk is from a 
different species, as when a child ingests cow's milk, al- 
though many observations have been made which indicate 
that antibodies are absorbed under such circumstances, 
if only to a limited extent. It would therefore appear 
that antibodies in cow's milk are of more value to the 
calf than to a child ingesting such milk. The absorption 
of antibodies from the intestines is greatest during the 
first few days after birth and decreases with age. In 
older animals, the antibodies are split up by digestion 
like other proteids. 

Germicidal Action of Milk. — ^Milk from cows in normal 
condition always contains antibodies which destroy many 
of the bacteria commonly present in milk. The intensity 
and duration of this germicidal action varies with the 
temperature. If the milk is kept at 37° C. (98.6° F.), 



44 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

there will be a decided decrease in the number of bacteria 
for the first six hours after the milk is drawn from the 
cow; at 26 to 29° C. (79 to 84° F.) the decrease is less 
rapid, but continues for eight to ten hours, and at 15° C. 
(60° F.) it is still further reduced in rate but continues for 
about twenty- four hours (Kosenau and McCoy). The 
effect of the same milk on -different species of bacteria is 
different, and the effect of different milks on the same 
species of bacteria also varies, showing that the antibodies 
are specific for certain species of bacteria. The germic- 
idal power of milk is not capable of destroying all bac- 
teria which may gain access to milk during milking and 
the subsequent handling ; hence precautions against bac- 
terial contamination together with proper cooling are 
none the less necessary. It is also incapable of always 
preventing the development of pathogenic bacteria. 
These organisms may enter the teat canal and milk cistern 
and even invade the gland alveoli. Heating milk for 
thirty minutes to 56° C. (133° F.) considerably weakens 
the germicidal property, and it is entirely destroyed by a 
temperature of 70° C. (158° F.), or above, for thirty 
minutes. Bacteria, therefore, grow more rapidly in 
heated milk than in fresh raw milk. The germicidal 
power of colostrum and of milk from cows affected with 
mastitis is greater than that of normal milk. 

Toxins. — It has been demonstrated that tetanus toxin 
may be eliminated in the milk of a cow affected with 
tetanus, and in sufficient quantity to kill mice fed with 
the milk (Miessner). There is, therefore, reason to be- 
lieve that other bacterial toxins are also eliminated in 
the milk, although there is no direct proof. However, 
the quantity of toxin circulating in the blood is very 
small, even in severely infected animals, and only a 



MILK 45 

minute quantity could be eliminated in the milk. When 
it is considered in addition that the milk secretion ceases 
in severely affected animals, the danger from toxins 
eliminated in the milk is very slight. Toxins may be 
produced by bacteria growing in milk after it is drawn 
from the udder. There is evidence to show that toxins 
are very readily absorbed through the gastro-intestinal 
mucous membrane of young animals. Toxins in milk 
from a different species are absorbed with much less 
facility than when the milk is from the same species. 
Diphtheria and tetanus toxins have been given to adult 
animals by the mouth in large quantities without any 
harmful effect, the toxins apparently being split up in 
the process of digestion like other proteids. These, how- 
ever, are soluble toxins (exogenous) which are more 
susceptible to chemicals and ferments than endotoxins. 
What may happen when the digestive processes are de- 
ranged, or when wounds are present in the mucous mem- 
brane, is not known. Milk from animals affected with 
rabies contains the virus of the disease, but such milk does 
not produce rabies when ingested if the mucous mem- 
brane of the digestive tract is intact and the gastric secre- 
tion is normal. 

Aggressins and other substances which inhibit the 
protective reaction of the body against the action of bac- 
teria and their toxins have also been demonstrated in 
milk. 

CLASSES OR GRADES OF MARKET MILK 

Until quite recently no effort was made to establish 
uniform grades or classes of milk. In some instances, 
the terms sanitary milk, hygienic milk, aerated milk, 
baby's milk, nursery milk, etc., have been applied by dis- 
tributers to some of the milk sold by them, but these 



46 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

terms are very indefinite and have been frequently used 
indiscriminately. Since 1893, milk produced under the 
supervision of a medical milk commission has been sold 
under the name of certified milk, but the term has also 
been applied to milk which was not produced under these 
conditions. The desirability of defining the special 
names used for milk, and the advantage to both the pro- 
ducer and consumer of grading or classifying market 
milk according to its hygienic quality, has long been 
recognized, but no definite steps were taken in the matter 
until 1907 when Melvin ^ proposed that market milk 
be graded in three classes, as follows : 

Class 1. Certified Milk. — This may be briefly defined as milk 
produced in accordance with the requirements of the American 
Association of Medical Milk Commissions (see Appendix). 

Class 2. Inspected Milk. — This term should be limited to 
clean raw milk from healthy cows, as determined by the tuber- 
culin test and physical examination by a qualified veterinarian. 
The cows are to be fed, watered, housed, and milked under good 
conditions, but not necessarily equal to the conditions provided 
for Class 1. All persons who come in contact with the milk 
must exercise scrupulous cleanliness, and must not harbor the 
germs of typhoid fever, tuberculosis, diphtheria, and other in- 
fections liable to be conveyed by the milk. This milk is to be 
delivered in sterilized containers, and is to be kept at a tempera- 
ture not exceeding 50 ° F. until it reaches the consumer. It shall 
contain not more than 100,000 bacteria per cubic centimetre. 

Class 3. Pasteurized Milk. — Milk from the dairies not able 
to comply with the requirements specified for Classes 1 and 2 
is to be pasteurized before being sold, and must be sold under 
the designation " pasteurized milk." Milk for pasteurization 
shall be kept at all times at a temperature not exceeding 60° F. 
while in transit from the dairy farm to the pasteurization plant, 

^ 24th Annual Report, U. S. Bureau of Animal Industry, 
pp. 179 to 182. 



MILK 47 

and milk after pasteurization should be placed in sterilized con- 
tainers and delivered to the consumer at a temperature not 
exceeding 50° F. All milk of an unknown origin should be 
placed in Class 3 and subjected to clarification and pasteuriza- 
tion. No cow in any way unfit for the production of milk for 
use by man, as determined upon physical examination by an 
authorized veterinarian, and no cow suffering from a com- 
municable disease should be permitted to remain on any dairy 
farm on which milk of Class 3 is produced, except that cows 
which upon physical examination do not show physical signs of 
tuberculosis may be included in dairy herds supplying milk of 
this class. This milk is to be clarified and pasteurized at cen- 
tral pasteurization plants, which shall be under the personal 
supervision of an officer or officers of the health department. 
These pasteurizing plants may be provided either by private 
enterprise or by the municipality, and should be located within 
the city. 

A further attempt at classification was made in 1911 
by a commission on milk standards appointed by the New 
York Milk Committee. This commission reconmiended 
that milk be graded in four classes, viz. : Class A, certi- 
fied milk or its equivalent; Class B, inspected milk; Class 
C, pasteurized milk, and Class D, milk not suitable for 
drinking purposes. A year later, however, the commis- 
sion presented a second report ^ in which the following 
classification was recommended: 

GEADE A 

Raw Milk. — Milk of this class shall come from cows free 

from disease as determined by tuberculin tests and physical 

examinations by a qualified veterinarian, and shall be produced 

and handled by employees free from disease as determined by 

^ Reprint No. 141 from the Public Health Reports, Aug. 22, 
1913. 



48 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

medical inspection of a qualified physician, under sanitary con- 
ditions such that the bacterial count shall not exceed 100,000 
per cubic centimetre at the time of delivery to the consumer. It 
is recommended that dairies from which this supply is obtained 
shall score at least 80 on the United States Bureau of Animal 
Industry score card. 

Pasteurized Milk. — Milk of this class shall come from cows 
free from disease as determined by physical examinations by a 
qualified veterinarian and shall be produced and handled under 
sanitary conditions such that the bacterial count at no time ex- 
ceeds 200,000 per cubic centimetre. All milk of this class shall 
be pasteurized under ofl5cial supervision, and the bacterial count 
shall not exceed 10,000 per cubic centimetre at the time of 
delivery to the consumer. It is recommended that dairies from 
which this supply is obtained shall score at least 65 on the 
United States Bureau of Animal Industry score card. 

The above represents only the minimum standards under 
which milk may be classified in Grade A. The commission recog- 
nizes, however, that there are grades of milk which are produced 
under unusually good conditions, in especially sanitary dairies, 
many of which are operated under the supervision of medical 
associations. Such milks clearly stand at the head of this grade. 

GRADE B 

Milk of this class shall come from cows free from disease 
as determined by physical examinations, of which one each year 
shall be by a qualified veterinarian, and shall be produced and 
handled under sanitary conditions such that the bacterial count 
at no time exceeds 1,000,000 per cubic centimetre. All milk of 
this class shall be pasteurized under official supervision, and the 
bacterial count shall not exceed 50,000 per cubic centimetre 
when delivered to the consumer. 

It is recommended that dairies producing Grade B milk 
should be scored and that the health departments or the con- 
trolling departments, whatever they may be, strive to bring 
these scores up as rapidly as possible. 



MILK 49 

GBADE C 

Milk of this class shaU corae from cows free from disease 
as determined by physical examinations and shall include all 
milk that is produced under conditions such that the bacterial 
count is in excess of 1,000,000 per cubic centimetre. 

All milk of this class shall be pasteurized, or heated to a 
higher temperature, and shall contain less than 50,000 bacteria 
per cubic centimetre when delivered to the consumer. 

Whenever any large city or community finds it necessary, 
on account of the length of haul or other peculiar conditions, 
to allow the sale of Grade C milk, its sale shall be surrounded 
by safeguards such as to insure the restriction of its use to 
cooking and manufacturing purposes. 

In 1917 the commission published a third report * in 
which the above-mentioned grades were again recom- 
mended with the same specifications for each grade ex- 
cept that the bacterial limit for Grade A, raw milk, was 
reduced from 100,000 to 10,000 bacteria per c.c. This 
is an extremely low bacterial limit for market milk to 
be used for general purposes and it is very doubtful if 
it can be adopted by any community without consider- 
ably reducing the supply of raw milk and increasing its 
cost to the consumer. Certified milk meets the demand 
for a milk of low bacterial content for special purposes, 
such as infant feeding, etc. 

1 Public Health Reports, Vol. 32, No. 7, Feb. 16, 1917. 



CHAPTEK IV 

BACTERIA OF MILK 

Unless drawn under special conditions, which are 
not obtainable in dairy practice, milk always contains 
bacteria. Some of them come from the udder ; others are 
derived from the cow's skin, the dust of the fodder and 
litter, the milk vessels and utensils, the person and cloth- 
ing of the milker, etc., and enter the milk during the 
process of milking and in the subsequent handling of 
the milk. They are, under normal conditions, non-patho- 
genic organisms, and, since they are always present in 
milk, are called the common milk bacteria. Under cer- 
tain conditions, which are discussed in another chapter, 
milk contains also pathogenic bacteria. 

COMMON MILK BACTERIA 

Some of the non-pathogenic bacteria do not bring 
about any perceptible change in milk. Many of them, 
however, produce marked alterations, and it is because 
of their presence that milk is so extremely perishable or 
unstable. In growing in milk, these organisms split up 
certain constituents, notably the lactose and casein, into 
various products, some of which are capable of exerting 
an injurious effect upon persons drinking the milk, par- 
ticularly children and invalid adults. Certain of these 
changes, including the more harmful kinds, may be con- 
siderably advanced before they are indicated by any alter- 
ation in the appearance, odor, or taste of the milk. There- 
fore, while the common milk bacteria are in themselves 
harmless, and while their growth in milk to a limited 
50 



BACTERIA OF MILK 51 

extent is not attended with any appreciable injurious 
effects, their presence in large numbers is not desirable 
because it may be accompanied by harmful results. 

There are numerous species of these organisms. For 
facility of study as well as for practical pm-poses, it is 
convenient to group them according to the changes which 
they bring about in milk. Although some of the species 
which ferment lactose produce both acids and gases, and 
although a part of those which act principally upon the 
lactose also operate upon the casein in a lesser degree 
and vice versa, nevertheless by grouping the different 
species according to their dominant effect a very clear 
conception is obtained of the important changes produced 
in milk by the organisms of each group. Following this 
plan, the numerous species of common milk bacteria may 
be classified in the following groups : 

1. Acid- forming Bacteria. — These organisms split 
up the lactose in milk and form acids. The milk first 
acquires a sour odor and taste and later curdles. This 
is the most quickly apparent change which occurs in 
milk. The acids combine with the calcium of the calcium 
caseinate, and the casein, being thus set free, is precipi- 
tated in the form of a smooth, white jelly-like curd, which 
may contain a few gas bubbles or furrows made by 
ascending bubbles. In the beginning, the curd is dry and 
is equal in size to the original volume of the milk, but 
later on it contracts and expresses a fluid or serum which 
holds in solution certain of the milk constituents. 

The time required for milk to sour and curdle depends 
upon the number and kind of acid-forming bacteria it 
contains and the temperature at which it is kept. On 
the average, about 0.45 per cent, acidity is necessary to 
bring about curdling. The acid-forming bacteria con- 



52 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

tinue to grow and to ferment lactose until the acidity 
reaches 0.8 per cent., but the growth of other bacteria 
stops when the acidity exceeds 0.2 per cent. The acid- 
forming bacteria, therefore, perform the very important 
service of inhibiting the growth of the more harmful 
bacteria. If their development is interfered with, the 
milk will undergo putrefaction instead of souring. 

Sour milk is net harmful to healthy adults; on the 
contrary, in certain forms (curds and whey, buttermilk, 
kefir, etc. ) it is a regular article of diet, and milk contain- 
ing certain acid-forming bacteria is beneficial in some 
diseased conditions. But, nevertheless, milk in which the 
fermentation is not sufficiently advanced to cause coagu- 
lation or even to produce an appreciable sour taste may 
cause vomiting and indigestion in small children and in 
persons affected with catarrh of the stomach. 

The usual cause of the spontaneous curdling of milk 
is the Bacterium lactis acidi ( Fig. 5) , also called Strepto- 
coccus lacticus, which occurs as a coccus or as a short oval 
or pointed bacterium, arranged in pairs, frequently in 
short and sometimes in long chains, and forms on solid 
media very small, white, circular or lenticular colonies, 
many of them being situated below the surface. In addi- 
tion to the difference in form, variations occur in the 
ability to ferment lactose and in other biological char- 
acters. These are regarded by some bacteriologists as 
changes due to environment, while others consider them 
a sufficient basis for recognizing the existence of different 
varieties or species. In general, however, organisms of 
the Streptococcus lacticus type ferment lactose more 
rapidly than the other species of acid-forming bacteria, 
forming principally lactic acid, with little or no gas. The 
milk has a clean, sour taste, while the fluid expressed from 



BACTERIA OF MILK 



53 



the curd is clear. Being commonly concerned in the 
souring of milk and producing principally lactic acid, 
the organisms of tliis type are known as the true lactic 
acid bacteria. The Streptococcus lacticus must not be 
confused with the mastitis streptococci (Fig. 6), which 
also ferment lactose and have other corresponding char- 
acteristics. The latter organisms grow in long, inter- 
twined chains, the individual members of which are rec- 
tangular or oval in form, with the long axis at right 





Fig. 5. — Preparation showing Streptococ- 
cus lacticus or Bacterium lactis acidi. 



FiQ. 6. — Preparation from sediment 
obtained by centrifugalizing milk from a 
cow affected with catarrhal mastitis, show- 
ing streptococci and leucocytes. 



angles to the length of the chain. On agar, they form 
extremely minute, punctiform, brownish colonies. 

The Bacterium acidi lactici (Hueppe) , also called the 
Bacillus lactis aerogenes, is frequently concerned in the 
spontaneous souring of milk, usually in association with 
the Streptococcus lacticus. This is a short, plump, non- 
motile bacterium which is closely related to the coli-aero- 
genes group of bacteria and may be regarded as the most 
active acid-forming member of that group. It grows 
upon the surface of solid media, forming thin, partially 
translucent, leaf-shaped colonies, or round semi-globular 



54 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

colonies. It ferments lactose more slowly and requires 
a higher temperature than the Streptococcus lacticiis. 
Acetic acid is the principal product of the lactose fermen- 
tation, although lactic and succinic acids and gas are 
also formed. Gas bubbles are rather numerous in the 
curd and the fluid expressed from the latter is not always 
clear. The sour taste of the milk is frequently un- 
pleasant. The Bacterium acidi lactici is regarded by some 
bacteriologists as a distinct species with strains showing 
differences resulting from environment and by others 
as the type of a number of species or varieties. The 
mastitis organisms, Bacillus Guilleheau {a and &), and 
some of the bacteria which produce slimy or viscid milk 
are closely related forms. 

Several varieties of long, thin, rod-shaped organisms, 
of which the Bacterium hulgaricu^ is a type, also form 
acid from lactose, but they operate so slowly at the usual 
temperatures that they are not a factor in the ordinary 
souring of milk. They are chiefly of interest because of 
their use in the preparation of the oriental milks (mazun, 
kefir, yoghurt) . The organisms of the Bacterium bul- 
garicus group are usually present in ensilage and those 
found in milk are no doubt derived directly or indirectly 
from this source. 

The temperature at which the milk is kept has an 
important influence upon the character of the lactose 
fermentation. In milk kept at 15 to 20° C. (59 to 68° 
F. ) , the organisms of the Streptococcus lacticus type will 
grow much more rapidly than those of the Bacterium 
acidi lactici type. The Streptococcus lacticus grows quite 
well at 15° C. (59° F.) and continues to grow at 10° 
C. (50° F.) , while the Bacterium acidi lactici grows bet- 
ter at higher temperatures and practically stops grow- 




Fig. 7. — Colonies of coli aerogenes bacteria (Weigmann). 




Fia. 8. — Colonies of Proieus vulgaris, natural size (Weigmann). 



BACTERIA OF MILK 55 

ing at 15° C. (59° F.). Keeping milk at a tempera- 
ture of 15° C. (59° F.) or below, therefore, inhibits the 
least desirable type of lactose fermentation. The Bacil- 
lus bulgaricus requires a temperature of at least 25° C. 
(77° F.). 

The acid-forming bacteria are widely distributed, but 
according to Esten ^ the chief primary source of those of 
the Streptococcus lacticus type found in milk is the cow's 
mouth. The organisms are present in the manger and on 
everything within reach of the cow's mouth, also in the 
fcBces. The acid-formers of the Bacterium acidi lactici 
type are derived from sugar-containing grain and roots 
like corn, beets, and carrots, especially when they are cut 
into small pieces, packed and fermented (ensilage) ; they 
are also contained in the faeces of cows (Weigmann). 
Milk vessels and utensils, and other things and places 
with which milk comes in contact become seeded with 
acid-forming bacteria when not properly cleaned and 
sterilized, and are usually the principal sources of con- 
tamination when these organisms are present in milk in 
excessive numbers. 

2. Gas- forming Bacteria. — Included in this group are 
the bacteria which ferment the lactose in milk and form 
gases in addition to acids. They also decompose the 
proteids to some extent, especially the casein (Fig. 7). 
Most of them belong to the large coli-aerogenes group 
of organisms. The milk is curdled in the form of a 
smooth, white, jelly-like curd, which is more or less per- 
meated with gas bubbles and is associated with some 
fluid. The aerogenes organisms form a greater quantity 
of acids and gases than the coli and they also form more 

^ " Bacterium Acidi Lactici and Its Sources," Storr's Agr. 
Expt. Sta. Bull. No. 59. 



56 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

lactic acid than the coh, but the latter are more active in 
proteid decomposition. Carbon dioxide, hydrogen, car- 
buretted hydrogen, and nitrogen are the gases produced, 
while the acids formed are lactic, acetic, and succinic. In 
the early stages of this change, the milk has a sweetish- 
som- refreshing taste and an odor that is not unpleasant, 
especially when the aerogenes bacteria are operating, but 
later the taste is unclean, while the odor is stable-like, and 
finally the taste becomes nauseating and salty and the 
odor is Hke that of decomposing manure and urine. Milk 
undergoing this form of fermentation and decomposition 
may prove harmful to persons drinking it, especially in- 
fants and adults with weak digestion. 

The principal representatives of this group of bac- 
teria are the Bacillus coli and the Bacillus aerogenes, also 
called Bacillus lactis aerogenes and Bacterium acidi lac- 
tici (Hueppe). The Bacillus coli is a short, thick, oval 
organism, which is motile, and which forms on solid media 
colonies which are usually flat, leaf-shaped and partially 
translucent, sometimes moist and globular. Some vari- 
eties render the milk alkaline and do not curdle it nor 
produce any other visible change; others peptonize the 
casein. Several varieties of coli are pathogenic, e.g., the 
bacilli of calf cholera, the Bacillus enteritidis (Gartner) 
and the Bacillus phlegmasia ilheris, which is one of the 
causes of parenchymatous mastitis according to Kitt. 
The Bacillus lactis aerogenes or Bacterium acidi lactici 
(Hueppe), described previously in connection with the 
acid-forming bacteria, may be regarded as a type of the 
aerogenes bacteria, of which there are a number of 
varieties. 

The optimum temperature of the coli-aerogenes bac- 
teria is 37° C. (98.6° F.), but they grow quite well at 



BACTERIA OF MILK 57 

lower temperatures down to 20° C. (68° F.). They do 
not grow as well as the Streptococcus lacticus between 
15 and 20° C. (59 and 68° F.), and at lower tempera- 
tures the diiFerence is still greater. 

These organisms are normal inhabitants of the in- 
testines of the cow and consequently are hardly ever en- 
tirely absent from milk. They are present in water pol- 
luted by drainage from barnyards, manure heaps and 
cesspools, and also on field crops, especially roots grown 
on manured ground. Their presence in milk in any 
considerable number indicates that it has been contami- 
nated with manure or with polluted water. 

Milk also contains anaerohic bacteria which ferment 
lactose and its salts, forming gas in large quantity and 
producing strong- smelling acids like butyric, valerianic 
and propionic. These organisms are present ordinarily 
in small number and their development is usually pre- 
vented by the acid-forming bacteria. When they grow 
in milk in large numbers, a curd containing many gas 
bubbles is formed. The milk has the odor of the acid 
produced and frequently an odor of putrefaction also. 
Because of the latter condition, these organisms are re- 
garded as putrefactive bacteria. The best known are 
those which produce butyric acid and are consequently 
called butyric acid bacteria. They are very large spore- 
forming bacilli which live in cultivated soil in symbiosis 
with the peptonizing bacteria. They are usually present 
in the spore-forming stage on the products of the field. 
Morphologically, they are distinguished from the other 
spore-forming milk bacteria by a change in form during 
spore formation, becoming shuttle-shape, drum-stick- 
shape, etc. 

Ayers and Johnson found gas-forming bacteria in 



58 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

milk which were not members of the coH-aerogenes group 
but which were apparently spore-formers, having sur- 
vived a temperature of 93.3° C. (200° F.) for thirty 
minutes/ 

3. Peptonizing or Casease Bacteria. — The bacteria 
of this group are also known as liquefiers and are the cause 
of decay and putrefaction in general. They secrete 
two enzymes or ferments which attack the proteids of 
milk, especially the casein. One is a rennet-like ferment 
which acts upon the calcium caseinate in the same manner 
as rennet, splitting it up into calcium paracaseinate and 
a substance called whey-proteid. The calcium para- 
caseinate being insoluble, it is precipitated and forms a 
curd. The whey-proteid remains in solution in the whey, 
hence the name. The other enzyme is casease, a proteo- 
lytic ferment resembling trypsin, which digests the pro- 
teids in the curd and whey, splitting them up into soluble 
compounds like albumoses and peptones (peptonization) 
and then again into simpler compounds like amino-acids 
and ammonium bases (decomposition). The two fer- 
ments are produced in varying proportions by different 
species of bacteria. When the rennet-like ferment pre- 
dominates a firm white curd is formed and is slowly 
digested. There is more or less fluid (whey) present. 
As digestion proceeds, the curd gradually disappears and 
is replaced by a turbid fluid. The surface of the curd in 
contact with the fluid has a rough or fuzzy appearance. 
When the proteolytic ferment (casease) is present in 
greatest quantity, the curd is soft, flocculent and 
" mushy," or coagulation does not occur at all, while 
peptonization takes place rapidly. In the earlier stages 

1 B. A. I. Bulletin No. 161, pp. 47 and 48. 



BACTERIA OF MILK 59 

of this type of decomposition, the milk acquires a bitter 
taste (peptones) and later the taste and odor are foul 
and unpleasant. Some of the decomposition products 
are capable of exerting an injurious effect upon persons 
drinking the milk. Nausea and vomiting may occur, 
even in adults, when the taste is only bitter and before it 
has become decidedly foul. The reaction of the milk is 
usually alkaline, but some of the peptonizers are acid- 
formers and curdle milk by souring it. 

Included in this group are certain of the cocci which 
appear to be constantly present in the lower parts of the 
cow's udder and are consequently called udder cocci. 
These organisms are to be found regularly in milk when 
it comes from the udder, especially in the fore milk. 
They are present in greater proportion in milk produced 
under good conditions than in ordinary milk. There are 
many varieties or species of these organisms which differ 
principally in their fermentative properties and in the color 
of their colonies. In milk hygiene, it is desirable to 
divide them into peptonizers and non-peptonizers. Part 
of the peptonizers first curdle milk and then digest the 
curd ; others bring about digestion without previous cur- 
dling. Some of the organisms which curdle the milk do 
so by means of a rennet-like ferment ; the others by means 
of acid resulting from fermentation of the lactose (acid 
peptonizers) . The non-peptonizers are practically inert, 
producing no apparent change in milk. On agar plates, 
the udder cocci form small, irregularly round colonies 
which are usually white. The colonies of Staphylococcus 
pyogenes albus vary from white to cream color, while 
those of Staphylococcus pyogenes aureus are orange- 
yellow. The latter two organisms are peptonizers and 
also form lactic acid. The ordinary udder cocci and 



60 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Staphylococcus pyogenes alhus and aureus are similar in 
so many respects that all are regarded by some bac- 
teriologists as different varieties of the same species. 
The optimum temperature for the udder cocci is 35 to 
37° C. (95 to 98.6° F.), but they grow well at much 
lower temperatures, development continuing down to 
freezing. The peptonizing action is exerted at these 
low temperatures. 

Many of the peptonizers are spore-forming bacteria. 
The most common representatives of this division are 
the hay bacillus (Bacillus suhtilis) and the potato bacillus 
(Bacillus mesentericus vulgatus). They belong to a 
large group of organisms which are very numerous in 
cultivated soil and are consequently found on all products 
of the soil, especially hay, straw, roots, etc. They are 
large rod-shaped bacteria with rounded ends. The spores 
form in the middle or end of the organism without chang- 
ing its shape. On agar plates these bacteria form dry, 
thin, superficial skin-like colonies, with irregular borders. 
The colonies have a tendency to extend over the surface 
of the media and are consequently called " spreaders.'* 
These organisms are very numerous in the dust of hay 
and other dry fodder, also in straw, and they may get 
into the milk in large numbers if the fodder or litter is 
brought into the stable and distributed a short time before 
milking, or if dust from hay or other dry fodder is per- 
mitted to sift down into the stable through cracks in the 
ceiling. When a cow lies upon bedding or upon loose 
soil, these bacteria enter the folds and creases of the 
skin and become attached to the hair, and when the cow 
is milked those upon the udder, flanks and surrounding 
parts are dislodged and may fall into the milk pail. 
These organisms are especially numerous on the hair 



BACTERIA OF MILK 61 

and skin of cows at pasture. The manure does not con- 
tain very many and few are carried into milk on this 
substance (Weigmann). The hay and potato bacilli 
grow best at 23 to 37° C. (73 to 99.6° F.), but will de- 
velop at any temperature between 10 and 45° C. (50 to 
113° F.) . The spores are very resistant to heat and will 
survive several hours boiling. 

Other peptonizers include the bacteria of the proteus 
group of putrefactive organisms, which are often present 
in milk, although more frequently found in water ( Fig. 
8). They are long, thin bacilli which grow in colonies 
of various forms. The most common representative of 
these organisms is the Bacillus pfoteus vulgaris, which 
grows in colonies with branches or ray-like projections. 
They get into the milk principally through the water used 
to wash the milk vessels and utensils. The Bacillus 
proteus vulgaris grows best at about 25° C. (77° F.) 

4. Alkali- forming Bacteria. — Some of the bacteria 
commonly found in milk render the milk alkaline without 
producing any change for a time in its appearance, taste, 
or odor. When the alkalinity has attained a certain 
degree, the fat is saponified and the neutral calcium 
caseinate compound becomes basic, in consequence of 
which the milk is changed to a yellow, translucent, whey- 
like fluid (Jensen). Within the ordinary life of milk, 
however, the bacteria of this group are practically without 
effect. Usually they get into the milk in the same man- 
ner as hay bacilli (page 60), their source being the soil, 
but occasionally they are derived from the faeces 
(Rogers). 

5. Inert Bacteria. — ^A large number of the common 
milk bacteria produce no change in the appearance, odor, 
taste, or reaction of milk and are consequently said to 



62 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

be inert. Many bacteria belong to this group, which in- 
chides some of the udder cocci. Many of the most im- 
portant pathogenic organisms are also inert in so far as 
their effect on milk is concerned, notably the tubercle 
bacillus, the bacillus of typhoid fever, paracoli or para- 
typhus bacilli, and the diphtheria bacillus. The presence 
of these harmful organisms is not indicated by any ap- 
parent change in the milk. 

VARIATIONS IN NUMBER AND KIND OF BACTERIA 
Different samples of market milk may show the 
greatest differences in the number and kind of bacteria 
present. One sample may contain much fewer than 1000 
bacteria per c.c. and another may contain four or five 
million and even more. In one sample, the bacteria may 
be largely of the inert forais and in another the bacteria 
of the gas-forming group may predominate. Market 
milk containing not more than 100,000 bacteria per c.c. 
is considered of good quality. The limit for certified 
milk is 10,000 bacteria per c.c. 

The kind or species of the bacteria must be considered 
as well as the number. Generally, the smaller the num- 
ber of bacteria present the better the milk, but there are 
exceptions to this rule. A few pathogenic organisms 
would be more harmful than a much larger number of 
the common milk bacteria. Between the different groups 
of the latter there are also important differences. Milk 
containing a rather large number of bacteria the greater 
proportion of which belong to the inert or lactic acid 
groups is less objectionable than milk containing a 
smaller number of bacteria with the greater proportion 
belonging to the gas-forming or peptonizing groups. On 
the other hand, while milk containing a large percentage 



BACTERIA OF MILK 63 

of peptonizing bacteria is not objectionable when the 
total number of bacteria is small, it is always objection- 
able when the bacterial count is high. 

The number of bacteria present in market milk de- 
pends upon (1) the original contamination, (2) the 
temperature at which the milk has been kept, and (3) 
the age of the milk, i.e.^ the time which has elapsed since 
the milk was drawn from the cow. 

1. By original contamination is meant the bacteria 
which get into the milk during milking and the subse- 
quent handling of the milk. The extent of this depends 
upon the cleanliness and health of the cows, stable prac- 
tices, method of milking, cleanliness of the milk vessels 
and utensils, etc. 

2. The temperature at which milk is kept affects not 
only the total number of bacteria but also influences the 
relative rate of increase of the different kinds or species. 
As a rule, the higher the temperature the more rapidly 
the bacteria multiply. For example, Conn found that 
when fresh milk contained 6525 bacteria per c.c, 
after 25 hours at 10° C. (50° F.) it contained 6425 bac- 
teria per c.c, while after 25 hours at 21° C. (70° F.) it 
contained 6,275,000 bacteria per c.c. 

When milk is promptly cooled to 10° C. (50° F.) 
and held at that temperature, little or no increase of 
bacteria will occur for twenty-four to thirty-six hours, 
and even at 15° C. (59° F.) the increase will not be 
very great. At temperatures above 20° C. (68° F.), 
however, the bacteria increase very rapidly. 

As stated above, the temperature affects not only the 
number of bacteria but also the relative development of 
the different species. In other words, it determines the 
type of fermentation or decomposition which the milk 



64 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

will undergo with age. Most species of bacteria thrive 
best at about body temperature (37 to 38° C, 98.6 to 
100.4° F.), but at lower temperatures some multiply 
more rapidly than others. At temperatures below 15° C. 
(59° F.), and especially below 10° C. (50° F.), the or- 
ganisms of the peptonizing group develop more rapidly 
than any of the other common milk bacteria. At 15 to 
20° C. (59 to 68° F.), the true lactic acid bacteria in- 
crease faster than any of the others. At temperatures 
above 20° C. (68° F.), the acid-forming bacteria may 
continue to multiply more rapidly than the others, but 
the gas-formers are more likely to increase most rapidly. 
The higher temperatures are also favorable to the de- 
velopment of pathogenic organisms. 

3. The age of milk has considerable influence on the 
number of bacteria. The longer the period which has 
elapsed since the milk was drawn from the cow the more 
time afforded for the multiplication of the bacteria in- 
cluded in the original contamination. 

( The method of determining the number of bacteria 
is described on pages 260 to 272.) 

Proportion of Different Groups of Bacteria. — The 
kind or species of bacteria included in the original con- 
tamination, and the relative proportion in which the 
different groups are represented, will vary with the con- 
ditions under which the milk is produced. In milk pro- 
duced under good conditions and examined shortly after 
it was drawn from the cows, Conn found that the greater 
portion of the bacteria are udder cocci, including both 
peptonizers and the inert variety. Usually 1 or 2 per 
cent., sometimes more, are lactic acid bacteria. A few 
gas-producing bacteria and hay and potato bacilli are 
likely to be present, but they should never be numerous. 



BACTERIA OF MILK 65 

The kind of bacteria which will predominate in milk of 
this kind when it reaches the consumer will depend upon 
the temperature at which it is kept (see above). The 
fermentation test offers a rapid and convenient method 
of determining the kind of bacteria which predominates 
in a sample of milk (see page 278) . 

A large percentage of the bacteria present in market 
milk belongs to the inert group. This is shown by the 
following table compiled from examinations reported by 
Ayers and Johnson * : 



No. samples 
esamined. 


Average 
number bac- 
teria per c. c. 


Percent, 
peptonizing. 


Percent. 
Alkali- 
forming. 


Percent, 
inert. 


Percent. 
Acid, coag- 
ulating. 


Percent. 
■ Acid, non- 
coagulating. 


12 


82,950,000 


17.31 


6.47 


29.31 


36.17 


10.71 


17 


3,451,000 


14.10 


19.66 


43.51 


12.98 


9.74 




24,700 


12.81 


3.33 


43.13 


33.85 


6.85 



1 B. A. I. Bull. 161, pp.20-27. 



CHAPTER V 

MILK DEFECTS 

In addition to the changes in milk caused by the 
common milk bacteria and those occurring in the course 
of diseases of the cow, there are certain alterations in 
consistency, odor, taste, and color which are known as 
milk defects. Some of these defects make the milk re- 
volting, even nauseating, while a few render it harmful. 
They may be divided into two groups (a) those which 
are present when the milk is drawn from the udder and 
(b) those which appear shortly afterward. 

(a) Milk Defects which are Present in Milk when it 
Comes from the Udder. — The most important of these 
are named below, together with the causes, the latter 
being given because they indicate the measures to be taken 
for the correction or removal of the defects. 

1. Cow-like or Salty, Cow-like Taste. — The milk iias 
a strong cow-like taste or a salty, cow-like taste, is of a 
gray color and may have the appearance of soapy water. 
This may be due to several causes. Milk from cows in 
the last stages of lactation has a mild, cow-like taste which 
is attributed to the relaxation of the gland tissue and fil- 
tration of blood serum between the epithelial cells of the 
alveoli. The cow-hke taste also occurs when the cow 
has been incompletely milked at the previous milking, 
and it is claimed that the first few streams of every milk- 
ing have a similar taste. In these cases it is thought that 
the abnormal taste is due to bacteria which enter the teat 
canal. Certain staphylococci and streptococci and some 
66 



MILK DEFECTS 67 

bacteria of the coli-aerogenes group give milk a cow-like, 
salty taste (Weigmann). 

2. " Fishy " Milk. — Milk from cows near the end of 
lactation may have a " fishy " taste. This defect is be- 
lieved to result also from feeding fish meal and from graz- 
ing cows on marshes subject to overflow with salt water; 
but cows have been fed on large quantities of fish meal 
without affecting the taste of the milk or butter. In one 
instance, the milk of one cow in a herd had such a pro- 
nounced " fishy " taste that it tainted the milk from the 
entire herd, although this cow was fed and stabled in 
exactly the same manner as the others. The cause in this 
case could not be determined. Milk may acquire a 
" fishy " taste from milk vessels which are rusted and 
also from those which have not been rinsed clean of the 
soap powder used in washing them. 

3. Hancid Milk. — A rancid odor and taste in milk as 
it comes from the udder may be due to the same condi- 
tions which give milk a cow-like taste. A rancid odor and 
taste may appear a short time after the milk is drawn 
from the udder as a result of the growth of butyric acid 
bacteria (page 57). On several occasions an unidenti- 
fied biscuit-shaped organism, growing in pairs, with the 
flat sides toward each other, has been found to be the 
cause of a rancid odor and taste. 

4. Slow-creaming Milk. — The milk is thicker and 
more viscous than usual ; the cream separates slowly and 
in less quantity than normal, sours slowly and does not 
" butter " readily. This defect has been observed in the 
milk from cows near the end of lactation and in milk from 
cows fed on beets, carrots, and turnips. Certain species 
of bacteria greatly increase the viscosity of milk, pro- 



68 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

ducing what is known as viscid, " ropy," or " stringy " 
milk (page 69). 

5. Premature curdling may occur in connection with 
distm-bances of digestion, udder diseases, advanced preg- 
nancy, overexertion and feeding sour brewers' grains 
and distillery slop ; it may also result from the develop- 
ment of excessive numbers of the acid-forming and 
peptonizing udder cocci as a consequence of incomplete 
milking. In the latter case, sodium bicarbonate or sali- 
cylic acid internally is recommended. 

6. ''Gritty" or ''Sandy" Milk.—SmsM granular 
particles, concrements of calcium and magnesiimi phos- 
phate, occur in milk when defects exist in the epithelium 
of the alveoli of the udder which permit the passage of 
the salts of the blood ; also when salts are present in the 
blood in excessive quantity as a result of the feeding of 
substances containing a high percentage of mineral mat- 
ter (Weigmann). These granules may be increased in 
size by the adhesion of mucus, epithelial cells, salts, etc., 
and form milk stones or udder stones (calculi), which 
may make milking difficult or painful. The calculi are 
of various shapes and sizes and may be as large as a bean. 

" Bloody " milk, the " flaky " milk occurring in mas- 
titis and the other changes associated with disease of the 
udder and other pathological conditions are considered 
in the chapter on the " Influence of Disease Upon Milk." 
For other defects, see also the remarks under odor and 
taste (page 28). 

(6) Milk Defects which Appear after the Milk is Drawn 
from the Udder. — The greater part of these defects 
are caused by certain species of bacteria, yeasts and 
fungi which grow well at low temperatures. Spring- 
houses, cooling-rooms and other dark, damp places fur- 



MILK DEFECTS 69 

nish an environment favorable to their development. 
Measures for the correction of these defects must be 
based upon the source of the organisms concerned. 

1. Bitter Milk. — Several species of bacteria, yeasts 
and fungi have been isolated at different times from bitter 
milk. In some instances the organisms responsible for 
the bitter taste were found in the udder. Milk may ac- 
quire a bitter taste from the action of the organisms 
belonging to the peptonizing and gas-forming groups of 
the common milk bacteria. This is especially true of 
heated milk, in which the spores of the soil bacteria (hay 
and potato bacilli ) survive. The occurrence of a bitter 
taste in milk is often associated with the feeding of cer- 
tain substances, notably mouldy or decomposed fodder, 
beet and turnip leaves, and raw potatoes ; also vetch, wild 
mustard and other cruciferous plants, leek, dog-fennel, 
tansy, etc. The use of mouldy or decomposed straw for 
bedding is accompanied by the same eff'ect. It is believed 
that the bitter taste is caused by organisms which are 
present on these substances and which enter the milk 
after it is drawn from the udder, and it is recommended, 
therefore, that these feeds be given after milking, except- 
ing, of course, those which are mouldy or decomposed. 
Another theory is that the taste is due to a bitter sub- 
stance which is ingested with the food and eliminated 
through the udder. If milk is stored in rusted vessels 
until a certain degree of acidity develops, it acquires a 
bitter, astringent taste, due to formation of iron lactate 
or acetate. Milk may also have a bitter taste just before 
parturition and near the end of lactation. 

2. Viscid, " Ropyf or " Stringy '' Milk.— The milk 
is thick and viscid and when it is poured from one vessel 
to another strings are formed ; it may also be drawn out 



70 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

into long strings with a rod or stick. The bacteria which 
cause this defect are frequently introduced into the milk 
by the water used to wash the milk vessels and utensils. 
Milk-houses, storage tanks, etc., may be infected by the 
same means. Water from streams and shallow wells 
receiving surface drainage, also from springs receiving 
surface or subsurface drainage, is especially likely to 
contain the organisms. They are also to be found on 
vegetation growing in low, damp places and on straw 
stored in a damp condition. In Sweden " stringy " milk 
is prepared artificially and is a popular article of food 
(tatmjolk), while, in Holland, Edam cheese is made 
from " stringy " milk produced by a certain organism. 

3. '' Soapy " Taste, — Milk may acquire a " soapy " 
taste from the action of bacteria which attack the proteids 
and fat of milk. Several species of these organisms have 
been found on straw and fodder. 

4. Failure to Sour and "Butter" — Milk may not 
sour and cream may not sour and '* butter " at all or only 
very slowly. This defect may be due to a deficiency in 
acid-forming bacteria or to an excess of peptonizers. In 
the latter case, the milk or cream usually has a bitter 
taste ; occasionally a " soapy " taste. Alkali-forming bac- 
teria, butyric acid bacteria, some of the organisms of the 
coli-aerogenes group and certain yeasts and fungi may 
also delay or prevent souring and " buttering." In some 
cases the cream foams when churned, in consequence of 
the formation of gas. This defect is especially liable to 
occur when cows are pastured on low, wet land; also when 
the leaves of roots (beets, etc.) , are fed, and in cold, wet 
weather. Cream from the milk of cows near the end of 
lactation will not " butter " sometimes because of the 
alkalinity of the secretion. 



MILK DEFECTS 71 

5. Stahle-like, turnip-like^, and heet-like tastes, and a 
burnt or malt-like taste and odor are each caused by cer- 
tain species of bacteria. 

6. Blue Milk, — The Bacillus cyanogenus, also called 
the Bacterium syncyaneum, produces a grayish color on 
the surface of milk and, when the milk is sour, blue spots, 
wliich may become confluent. There are several other 
species of bacteria which produce a blue color in milk. 

7. Red 3Iilk.—-Red spots or a diffuse red color on the 
surface are produced by the Bacillus prodigiosus, also by 
SarciTia rosacea and several other species of organisms. 
The Bacterium lactis erythrogems curdles milk, then 
dissolves the curd and colors the fluid diffusely red. 

8. Yellow- or orange-colored spots are produced 
usually by the Bacillus synxanthus; also by the Sarcina 
lutea, Sarcina flava and the Bacterium fulvum. 

9. A yellowish-green discoloration is produced by the 
Bacillus pyocyaneu^. 

10. Greenish-yellow spots and diffuse discoloration 
may occur in sour milk as a result of the growth of the 
Bacillus fluorescens. 

11. Violet- colored spots are produced by the Bacillus 
violaceuSj, Bacterium janthinum. Bacillus lividus and 
Bacterium amethystinus. 

In some cases, although very rarely, these pigment- 
forming bacteria are present in the udder. Usually, they 
enter the milk after it is drawn from the udder. They 
can generally be excluded by sterilizing the milk vessels 
and cleaning and disinfecting the places where the milk 
is stored; sunning it also if possible. Sometimes it will 
also be necessary to clean and disinfect the stable and to 
see that the cows are thoroughly cleaned before milking. 



CHAPTER VI 

INFLUENCE OF DISEASE UPON MILK 

Man is susceptible to several of the specific infectious 
diseases of cattle viz: tuberculosis, aphthous fever or 
foot and mouth disease, cowpox, anthrax, rabies, and 
actinomycosis. Furthermore, mastitis, calf cholera, acute 
croupous and hemorrhagic enteritis (paracoli infection), 
septic metritis, and many suppurative conditions in cattle 
are caused by bacteria which are pathogenic for man. In 
certain non-bacterial affections, such as gastro-intestinal 
catarrh, the milk sometimes becomes unpalatable and, 
when ingested, may cause irritation of the gastro-intes- 
tinal tract, especially in children. 

The study of the conditions under which disease-pro- 
ducing organisms enter the milk and the effect of disease 
upon the milk secretion is one of the important divisions 
of milk hygiene. Bacteria or virus may be carried by the 
blood to the udder and be eliminated with the milk, or 
they may be excreted through one of the other normal 
open channels or discharged from wounds and enter the 
milk after it is drawn from the udder. The first method 
is called direct infection and the latter secondary infec- 
tion. There is no doubt that bacteria circulating in the 
blood may pass over into the milk when the tissue sepa- 
rating the udder alveoli and tubules from the capillaries 
is broken down by disease. Some investigators are of 
the opinion that this may also occur when the udder tissue 
is intact, but this view is disputed by others. When 
bacteria invade the udder through the teat canal, as 

72 



INFLUENCE OF DISEASE UPON MILK 73 

occurs in the non-tuberculous forms of mastitis, they 
are, of course, always eliminated in the milk. 

In considering the influence of disease of the cow on 
market milk, the effect of dilution must not be overlooked. 
Milk from a diseased cow may be injurious when ingested 
by itself, but when it is mixed with the milk from a nimi- 
ber of other cows in a normal condition it may be 
so diluted as to render it harmless. The character of the 
mixed milk in this respect will depend partly upon the 
proportion of diseased cows to those in health, partly 
upon the ability of the organism concerned to grow in 
milk, and the temperatui'c at which the milk is kept. 

The diseased conditions affecting milch cows which 
are of importance in milk hygiene will now be considered 
separately. 

I. Diseases of Cattle Transmissible to Man 
Through Milk 

TUBERCULOSIS 

In milk hygiene there are four points to be considered 
in connection with tuberculosis: (1) The frequency of 
tubercle bacilli in market milk, (2) the virulence for 
man of tubercle bacilli from cattle, (3) the conditions 
under which milk is infected with tubercle bacilli by 
tuberculous cows, and (4) how can contamination of 
market milk with tubercle bacilli be prevented. 

1. The Frequency of Tubercle Bacilli in Market Milk. — 
In a number of cities in this country and abroad, samples 
of market milk have been collected and examined for 
tubercle bacilli. Anderson* examined 233 samples in 
Washington in 1906 and found tubercle bacilli in 6.72 

1 U. S. Hygienic Lab. Bull., No. m, pp. 167-197. 



74 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

per cent. In Philadelphia, in 1908, Campbell ^ examined 
130 samples of raw milk and found tubercle bacilli in 
13.8 per cent.; twelve samples of milk sold as " pasteur- 
ized " were also examined by him and one sample, or 8.3 
per cent., contained virulent tubercle bacilli. Hess ^ 
found tubercle bacilli in 16 per cent, of the samples he 
examined in New York in 1909, and of 144 samples ex- 
amined by Tonney in Chicago in 1910 10.5 per cent, were 
infected with tubercle bacilli. In Germany, from 16.5 
to 27.1 per cent, of ;:he samples of market milk examined 
in various cities contained tubercle bacilli; in England, 
10 to 25 per cent. ; in Paris, 20 per cent., and in Copen- 
hagen, 4 per cent.^ Another evidence of the frequency 
of tubercle bacilli in milk is the general virulence of sep- 
arator milk from creameries. This milk has been found 
to be such a great factor in the dissemination of tubercu- 
losis among calves and hogs that several states, among 
them Pennsylvania, have passed laws requiring such milk 
to be pasteurized before it is removed from the creamery 
to be fed to cattle or swine. 

There are no statistics which show definitely the ex- 
tent to which tuberculosis exists among dairy cattle in 
the United States. The disease is found in less than 1 
per cent, of the cattle slaughtered for meat under Federal 
inspection, but the greater proportion of these are beef 
cattle and many of them are of young age, a period when 
tuberculosis is not as frequently found as in later life. 
The proportion of dairy cows affected with tuberculosis 
is not known. The per cent, of infected animals varies 

2 26th Annual Report, B. A. I., pp. 175-177. 
^ The Incidence of Tubercle Bacilli in New York City Milk, 
Jour. Am. Med. Assoc, No. 13, Vol. 52. 
4 Rievel, Milchkunde, pp. 99-100. 



INFLUENCE OF DISEASE UPON MILK 75 

greatly in different localities and in different herds 
in the same section. The proportion of animals reacting 
to the tuberculin test ranges from none in herds which 
have been subjected to annual tests for several years to 
30 per cent, and over in herds in which no effort has been 
made to control the disease. 

2. Virulence for Man of Tubercle Bacilli from Cattle. — 
— Until 1901 it was very generally accepted that tuber- 
culosis in man and animals was the same disease, although 
Theobold Smith, in 1896, and, subsequently, others, 
pointed out important differences in virulence, morphol- 
ogy, and cultural characteristics between bacilli from 
human and bovine sources. In 1901 Koch announced 
that tuberculosis of cattle was so rarely transmitted to 
man that it could practically be disregarded in formulat- 
ing plans to protect man against the disease. This an- 
nouncement was based on the failure of Koch and Schiitz 
to infect calves and other animals with tuberculous ma- 
terial from man, and upon post-mortem statistics col- 
lected by them of a number of cases of tuberculosis in man 
which happened to include only a small proportion of in- 
dividuals showing primary lesions in the digestive tract 
or attached lymph glands. Koch's announcement made 
a pronounced impression upon the general public, al- 
though his experiments were not original nor were his re- 
sults undisputed. Theobold Smith, Frothingham, and 
Dinwiddie in this country, and Piitz, Gaiser, Nocard, 
McFadyean, Thomasson, Chauveau, Klebbs, Kitt, Bol- 
linger, and Crookshank abroad, had previously at- 
tempted to infect cattle with tuberculous material from 
man and had succeeded in doing so, although they found 
that these animals were less susceptible to human tuber- 
culous material than to that from bovine sources. Since 



76 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Koch's announcement was made, some thirty-five or forty 
investigators in diiFerent parts of the world have at- 
tempted to transmit human tuberculosis to cattle and 
all have succeeded but one. 

As to the other point upon wliich Koch based his views, 
the frequency of primary tuberculosis of the digestive 
tract or attached lymph glands, we learn from the in- 
vestigations of others that, while this form of tuberculosis 
is rare in adults, the proportion of cases found in children 
by different investigators is extremely variable, ranging 
from % to 37.8 per cent. ; consequently the statistics col- 
lected by any one or two men cannot be accepted as 
representing the percentage of cases in which the lesions 
are primary in the digestive tract or attached lymph 
glands. Evidence has also been produced by the experi- 
ments of Mohler, Ravenel, Calmette, and others that 
tubercle bacilli may be introduced through the digestive 
tract and primary lesions established in the lungs or 
thoracic lymph glands without producing any lesions in 
the intestines or mesenteric lymph glands. 

Koch's views were not accepted by many of those who 
had made a special study of tuberculosis, and his an- 
nouncement instigated a vast amount of research work. 
Commissions were appointed by the British and German 
governments to investigate the relation of bovine to 
human tuberculosis, and other official bodies, and many 
individuals also took up the study of the subject. Koch 
contended that it could be assumed that the infecting 
material had been ingested with the food only when 
primary lesions were found in the digestive tract or its 
attached lymph glands, and that only those cases in which 
tubercle bacilh of the bovine type were demonstrated in 
the lesions could be regarded as having been infected by 



INFLUENCE OF DISEASE UPON MILK 77 

the products (meat and milk) of tuberculous animals. 
The investigations were therefore largely directed along 
these lines. The present views of those who have studied 
the subject are fairly represented by the conclusions 
reached by the British commission and published in 1911 
after a careful and thorough inquiry extending over ten 
years. These conclusions are as follows: 

*' There can be no doubt that a considerable propor- 
tion of the tuberculosis affecting children is of bovine 
origin, more particularly that which affects primarily the 
abdominal organs and the cervical glands. And, fur- 
ther, there can be no doubt that primary abdominal tuber- 
culosis as well as tuberculosis of the cervical glands is 
commonly due to ingestion of tuberculous infective 
material." One hundred and eight cases of human tuber- 
culosis other than lupus were examined by the Commis- 
sion and bacilli of the bovine type were found in twenty- 
four, or 22 per cent. The latter included sixteen cases 
of primary abdominal tuberculosis, three of tuberculosis 
of the cervical lymph glands, two of pulmonary tubercu- 
losis, two of tuberculosis of the bronchial lymph glands 
and one of joint tuberculosis. Bacilli of the bovine type 
were found in nearly half of the fatal cases of primary 
abdominal tuberculosis. 

The German commission made a study of fifty-six 
different cultures obtained from cases of tuberculosis in 
man and found six, or more than 10 per cent., to be of 
the bovine type. 

Park and Krumwiede ^ determined the type of bacilli 
present in 487 cases of tuberculosis in man and collected 
from the literature the records of 1033 cases in which the 

^ Journal Med. Research, pp. 109-114, vol. 27. 



78 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

type of the organism was determined by others, a total of 
1511 cases. There were 955 cases in individuals over 16 
years of age, 177 in children between 5 and 16 years, and 
368 in children under 5. Tubercle bacilli of the bovine 
type were found in 35 per cent, of the cases in children 
between the ages of 5 and 16, and in 26 per cent, of the 
cases in children under 5. In addition to these, there were 
eleven cases in which both types of bacilli were found. 

It is usually difficult to discover the source of infec- 
tion in cases of tuberculosis in man because the disease 
does not become apparent for a long time after exposure 
to infection has occurred. Nevertheless, there are a 
number of cases recorded of tuberculosis in children and 
adults using milk from tuberculous cows for which no 
other source of infection could be found.® Regarding the 
evidence in these cases as generally incomplete, Koch, in 
1902, suggested that a search be made for cows in which 
tuberculosis of the udder could be positively diagnosed 
and, when such cases were found, that it be ascertained 
how long the disease had existed, who consumed the milk 
or its products, whether the milk was used raw or cooked, 
and if the persons who used the milk or its products were 
infected with tuberculosis. Between 1905 and 1909 
Weber and Ungerman'^ found in Germany 69 cases of 
udder tuberculosis concerning which the information de- 
sired could be obtained. Three hundred and sixty per- 
sons, including 151 children, used milk from these cows. 
Two boys were aif ected with tuberculosis of the cervical 
lymph glands in which bacilli of the bovine type were 

6 Rievel, Milchkunde, pp. 107-108. 

"^ Cited by Ostertag, Zeitschr. fiir Fleisch u. Milchhyglene, 
pp. 26 and 27, No. 2, vol. xxiii ; p. 123, No. 6, vol. xxiv. 



INFLUENCE OF DISEASE UPON MILK 79 

demonstrated. Six other children and one adult were 
found with swelling of the cervical lymph glands, four 
children and one adult showed symptoms indicative of 
abdominal tuberculosis and one child suffered from 
scrofula, but in these cases no material could be obtained 
for bacteriological examination. Forty-one other persons 
showed various sj^mptoms of disease, but tubercle bacilli 
could be demonstrated in only 4, and these bacilli were of 
the human type. The other 304 individuals who had used 
milk from the tuberculous udders, or products made from 
such milk, showed no symptoms of disturbed health in 
1910. Subsequently, one of these, a girl, developed a 
peritonitis for which the infected milk was probably re- 
sponsible. While in some instances the milk was heated, 
mixed with milk from apparently healthy cows, or only 
a small quantity was used in tea or coffee, nevertheless the 
results of this investigation would indicate that a con- 
siderable amount of infectious material and favorable 
accessory conditions are required to infect man with 
bovine tuberculosis. But, as Weber himself has pointed 
out, it must be remembered that it is not known positively 
that the individuals manifesting symptoms suspicious of 
cervical lymph gland and abdominal tuberculosis were 
not actually infected, nor how many of the apparently 
healthy persons concerned were affected with lat- 
ent tuberculosis which may later, under some debilitat- 
ing influence, become active and progress to a fatal 
termination. 

Furthermore, Weber's observations are not confirmed 
by others who have studied the frequency of the trans- 
mission of bovine infection to man by milk. "A. comparison 
of the occurrence of tuberculosis in breast-fed children 



80 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

with the frequency of the disease in children receiving 
cow's milk was made by Sobotta. Of 80 exclusively 
breast-fed children, 17.5 per cent, were infected with 
tuberculosis ; of 57 children receiving cow's milk in addi- 
tion to mother's milk, 35.1 per cent, were infected, and 
of 30 fed exclusively on cow's milk 41 per cent, became 
tuberculous.^ Mitchell ^ examined 72 cases of cervical 
gland tuberculosis in the Children's Hospital in Edin- 
burgh and found tubercle bacilH of the bovine type in 
65, or 90 per cent. These children came from districts 
in which the cattle are extensively infected with tuber- 
culosis and most of them had been nourished on cow's 
milk. Of 70 cases of tuberculosis of the bones and joints 
in children examined by Fraser ^ in Edinburgh, 41, or 
60 per cent., were due to bacilli of the bovine type and in 
the greater number of cases the history indicated that the 
infection was introduced by cow's milk. In 261 cases of 
bone and joint disease examined by Eastwood and 
Griffith,^ '^ bacilli of the bovine type were found in 55, or 
21.1 per cent. Of these latter, 29 per cent, were from 
patients under 10 years of age and 9.4 from patients 
over that age. Seventeen cases of genito-urinary dis- 
eases were examined. Bacilli of the bovine type were 
found in three cases of kidney disease in persons 25, 19 
and 20 years old, respectively. Twelve and one-half per 
cent, of the fatal cases of tuberculosis in children under 
5 years old studied by Park and Krumweide ^^ were 



^ Cited by Rievel, Milchkunde, p. 110. 

^ Cited by Ostertag, Zeitschr. fiir Fleisch u. Milchhygiene, 
69, No. 3, vol. 24; p. 118, No. 5. vol. 24. 

10 Journal of Hygiene, pp. 257-309, 310-314, No. 2, vol. 15. 

11 Jour. Med. Research, pp. 109-114, vol. 27. 



INFLUENCE OF DISEASE UPON MILK 81 

due to bovine infection. They had nine cases in a found- 
ling asylum in children under 6 years who were nourished 
exclusively on cow's milk and found bovine infection in 
five, or over 50 per cent. Of the fatal cases in the Babies' 
Hospital in New York City 6% per cent, were due to 
bovine infection. 

These observations cannot be ignored in considering 
the results of Weber and Ungermann's investigation, 
especially since they all indicate that bovine tuberculosis 
is a considerable source of infection for children and are 
also in accord with the results of other studies of the 
disease. 

3. Conditions under which Milk is Infected with Tubercle 
Bacilli by Tuberculous Cows. — The milk of individual cows 
affected with tuberculosis in various forms has been 
tested for the presence of tubercle bacilli by injecting 
it into guinea pigs and by feeding it to these animals. 
Numerous experiments of this kind have been conducted, 
and upon the basis of these experiments tuberculous cows 
may be divided into three classes as regards the infectious- 
ness in their milk, viz: (a) Cows affected with tubercu- 
losis of the udder; (b) cows with apparently normal 
udders but showing clinical symptoms in other organs or 
parts, and (c) cows which do not show any clinical symp- 
toms but which have reacted to the tuberculin test. 

(a) Cows Affected with Tuberculosis of the Udder. 
— When the udder is tuberculous, tubercle bacilli are 
eliminated in the milk. In advanced or extensive cases 
of this form of the disease, the milk is very infectious ; it 
contains from 50,000 to 100,000 and even 1,000,000 
tubercle bacilli per c.c. (Ostermann), and remains viru- 
lent when injected into guinea pigs after it has been 
6 



82 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

diluted one billion times (Ostertag).^^ In the initial 
stages, when the tuberculous areas in the udder are small 
and isolated, the tubercle bacilli are less numerous, num- 
bering about 1000 per c.c. While such milk must be 
diluted about 1000 times to render it non- virulent when 
injected into guinea pigs, it may be repeatedly fed to 
them undiluted without producing tuberculosis. 

As to the frequency of tuberculosis of the udder, in 
the post-mortem examination of 1200 cattle reacting to 
the tuberculin test, nearly all of which were dairy cows, 
Pearson found the udder tuberculous in 104, or 5.75 per 
cent. Ostertag estimates that the disease is present in 
the udder of 0.1 to 0.3 per cent, of all cows. In consider- 
ing the frequency of tuberculosis of the udder, the large 
number of bacilli present in the milk in advanced cases 
must be remembered. The milk of one cow affected with 
advanced or extensive tuberculosis of the udder can infect 
thousands of quarts of milk from other cows, if mixed 
with it, and may even render the entire supply of a 
small town infectious. 

(h) Cows with Apparently Normal Udders but 
Showing Clinical Symptoins in Other Organs or Parts. — 
Milk from cows in this condition frequently contains 
tubercle bacilli. It appears very probable that the udder 
is actually diseased when tubercle bacilli are eliminated 
in the milk of such cows. The udder may be tuberculous 
and yet be apparently normal. The disease is always 
extensive when clinical symptoms are present, and 
usually it is generalized — tubercle bacilli have repeatedly 
invaded the blood stream and have had abundant oppor- 

12 Zeitschr fur Fleisch u. Milchhy., pp. 26 and 27, No. 2, 
vol. xxiii. 



INFLUENCE OF DISEASE UPON MILK 83 

tiinity to locate in the udder and to produce small, fresh 
tubercles, too small to be discovered by palpation of the 
udder. Such lesions may even escape observation on 
post-mortem examination because of their similarity in 
appearance to the actively secreting udder tissue. Rick 
found the udder tuberculous in 17.6 per cent, of the cases 
of generalized tuberculosis examined by him. Joest and 
Kracht ^^ found the supramammary lymph glands tuber- 
culous, when tested by inoculation, in 50 per cent, of the 
cases examined by them of generalized tuberculosis in 
which the udder did not show any clinical symptoms or 
macroscopic lesions on post-mortem examination; some 
of the lymph glands were slightly enlarged but otherwise 
they were of normal appearance. In one-half of these 
cases the udder tissue was also infected. It would there- 
fore appear that the udder is much more frequently tuber- 
culous in cases of generalized tuberculosis than is gener- 
ally suspected. 

Contradictory views exist as to the possibility of 
tubercle bacilli passing through the sound udder. Oster- 
tag and Prettner injected tubercle bacilli intravenously 
into cows with sound udders and found the milk non- 
virulent when inoculated into guinea pigs. 

Milk may be infected secondarily with tubercle bacilli 
when open tuberculosis is present in the lungs, intestines, 
or uterus. Cows affected with open tuberculosis of the 
lungs swallow the greater part of the infected material 
coughed up, and it passes out with the faeces ; the tubercle 
bacilli are not destroyed by the digestive secretions and 
remain virulent. Schroeder *^ and the British tubercu- 

^^ Joest and Kracht, Zeitschr. fiir Infectionskrank., etc., 
pp. 315-316, vol. 12, No. 4, 1912. 

14 Schroeder, p. 120, 25th Annual Report B. A. I. 



84 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

losis commission found the faeces infectious from tuber- 
culous cows which did not show any ch"nical symptoms, 
but these results have not been confirmed by others. 
Titze, Thieringer and Jahn ^^ demonstrated tubercle 
bacilli in the faeces of cows affected with open pulmonary 
tuberculosis, but not in the faeces of reacting cows wliich 
did not show clinical symptoms. Traum ^^ inoculated 
guinea pigs with fecal material from 36 cows, " prac- 
tically all tuberculin reactors," and none of the guinea 
pigs was infected with tuberculosis, although two of the 
cows exhibited physical symptoms of disease of the lungs. 
These results correspond with those obtained when 
samples of mixed milk from herds known to be infected 
with tuberculosis have been examined for tubercle bacilli. 
For example, O. Miiller examined samples of milk from 
1598 herds in East Prussia and tubercle bacilli were 
demonstrated in the samples from only 97 herds, al- 
though non-clinical reactors were present in the other 
herds. In the 97 herds from which the samples contain- 
ing tubercle bacilli were obtained, cows were found which 
exhibited clinical symptoms of udder tuberculosis or 
other forms of the disease. Similar results could be 
cited, lleichel ^^ found the faeces infectious from cows 
which were not tuberculous but which were stabled with 
cows affected with open tuberculosis. It therefore ap- 
pears probable that the sputum coughed out by cows 
with open tuberculosis, or the fine spray expelled from 
the mouth in coughing, may contaminate the feed of other 

^"^ Arbeit. K. Gesundheitsamt, pp. 1-34, No. 1, 1913. 
•^® Annual Report University of California Expt. Station, 
1915, p. 40. 

^^ Verbal communication. 



INFLUENCE OF DISEASE UPON MILK 85 

COWS and that these cows may ehminate virulent tubercle 
bacilli in the fasces even when they are not infected with 
tuberculosis. The presence of the bacilli in the fasces of 
tuberculous cows without open lesions in the lungs or 
intestines and without disease of the liver may be ex- 
plained on the same basis. Titze and Jahn found that 
in tuberculosis of the liver virulent tubercle bacilli may 
be excreted in the bile and eliminated with the fseces, tlius 
confirming the earlier findings of Joest and Emshoff. 
The udder and posterior parts of the cows affected with 
open tuberculosis become soiled with the infected faeces 
or vaginal discharges, and particles of this material drop 
off into the milk during milking, thus infecting the milk 
secondarily. The demonstration of tubercle bacilli in 
the milk of individual cows does not therefore necessarily 
indicate that the bacilli were excreted through the udder. 
Milk from cows with open tuberculosis usually contains 
about 1000 tubercle bacilli per c.c. While it does not 
always produce tuberculosis when fed to guinea pigs, or 
even when injected into them, it is often infectious and 
must therefore be regarded as dangerous. 

(c) Cows which do not Show any Clinical Symp- 
toms hut which have Reacted to the Tuberculin Test 
(Non-clinical Reactors), — The experiments with indi- 
vidual milk from cows which had reacted to the tuberculin 
test, but which did not show any clinical symptoms of the 
disease, have given contradictory results. Ostertag, 
Brauer, Ascher, Miiller, Stenstrom, Bassett, and others 
have found the milk from non-clinical reactors to be free 
from tubercle bacilli, while Rabinowitch and Kempner, 
Schroeder, Bavenel, Mohler, Martel, Guerin, DeJong, 
Moussu, and Fay have found tubercle bacilli present in 
milk from such cows. Ostertaf? tested the milk of 49 



86 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

non-clinical reactors and not a single sample produced 
tuberculosis when in j ected into guinea pigs. Later, in con- 
junction with Brauer,^^ he made a thorough test of the 
milk from 10 non-chnical reactors, inoculating guinea 
pigs, and feeding guinea pigs, calves and pigs. Not one 
of the experimental animals developed tuberculosis. 
Some of the guinea pigs in the feeding experiment re- 
ceived 66 grammes of milk daily for 5 months, or 33 times 
their body weight; 10 calves received 7 to 12 litres each 
day for 8 to 11 months and 20 pigs were given 1 to 6 
litres daily for 4 months. O. Miiller made inoculation 
tests on guinea pigs with the milk from 9 non-clinical 
reactors, and Ascher with the milk from 7, and tubercle 
bacilli were not demonstrated in a single case. Ostertag 
contends that in those cases in which tubercle bacilli were 
demonstrated in the milk from non-clinical reactors, the 
milk was infected secondarily, and in support of this 
view he points out that in some of the cases in which 
tubercle bacilli were demonstrated in the milk no lesions 
of tuberculosis could be found on postmortem, while in 
other cases lesions of open tuberculosis were present. At 
any rate, the evidence in its entirety indicates that the 
milk of non-clinical reactors is much less likely to contain 
tubercle than the milk of cows with tuberculous udders 
or which show clinical symptoms of the disease in other 
organs. 

Influence of Dilution, — While these experimental re- 
sults indicate very accurately the conditions under which 
tuberculous cows contaminate milk, it must not be for- 
gotten that they relate to the milk of individual cows 
tested separately, while in practice the milk of tuber- 



18 Zeitschr. fiir Fleisch u. Milchhy., p. 80, No. 4, vol. xxlv. 



INFLUENCE OF DISEASE UPON MILK 87 

culous COWS is diluted more or less with the milk of non- 
infected cows. The extent of the dilution will depend 
upon the method of handling the milk. Ordinary mar- 
ket milk, however, is frequently the mixed milk of sev- 
eral herds, but at any rate it is the mixed milk of a number 
of cows in the same herd. It has been demonstrated that 
the milk of cows affected with advanced or extensive 
tuberculosis of the udder may render the entire supply 
infectious when mixed with milk from other cows which 
are not tuberculous ; but this is not true of milk from cows 
which do not show clinical symptoms of the disease. 
Miiller and Hessler examined by inoculation samples 
of mixed milk from 2949 herds, each sample representing 
the milk from 30 to 200 cows. Tubercle bacilli were 
present in the samples from 156 herds. All of these 
herds except five were found to contain cows affected 
with udder tuberculosis or other forms of open tuber- 
culosis. In the five herds in which tuberculosis was not 
established clinically, Hessler is of the opinion that the 
tubercle bacilli were eliminated in the faces by cows with 
incipient cases of open lung tuberculosis which had not 
yet become perceptible. The other 2793 herds, in the 
milk samples from which tubercle bacilli were not demon- 
strated, certainly contained a considerable number of 
cows which would have reacted to the tuberculin test, 
judging from the extent to which tuberculosis was known 
to exist in the district in which they were located. 

Delepine examined the milk from 1385 farms and 
found tubercle bacilli in the samples from 294 farms. 
The cattle on 276 of these farms were examined and on 
190 farms one or more cows were found affected with 
tuberculosis of the udder, a bacteriological examination 
of the individual milk being necessary in some cases to 



88 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

discover the condition. After these cows were removed, 
the milk from these farms ceased to infect guinea pigs. 
No clinical cases of udder tuberculosis were found in the 
other 86 herds examined, but on these farms cows had 
been sold between the time the milk samples were col- 
lected and the herd was examined, or the farmer had been 
buying milk from other sources when the samples were 
collected. 

Friis inoculated guinea pigs with samples of mixed 
milk from 28 dairy farms in and about Copenhagen and 
demonstrated tubercle bacilli in the samples from four 
farms. On one of these farms two cows with tuberculosis 
of the udder were found and one cow with udder tuber- 
culosis was found on another, vdiile on the other two 
farms cows were found showing physical symptoms of 
tuberculosis in other organs. There is no doubt that the 
other twenty- four farms contained cows which would have 
reacted to the tuberculin test. 

The milk from 12 non-clinical reactors was tested for 
tubercle bacilli by Klein and Campbell by injection into 
guinea pigs. These cows were in a stable with 12 other 
non-clinical reactors which were not included in the ex- 
periment because they v\^ere approaching the end of the 
lactation period. The stable was light, well- ventilated, of 
suitable size and clean. The cows were cleaned with a 
curry-comb and brush and the udders wiped with a damp 
cloth before each milking. All the cows in the stable were 
examined by inspection, palpation and auscultation when 
the experiment began and no symptoms indicating tuber- 
culosis were found. They were all in a good, thrifty 
condition and none had a chronic cough. (All suspici- 
ous animals had been previously removed.) The 12 cows 
used in the experiment were arranged in groups of three 



INFLUENCE OF DISEASE UPON MILK 89 

each according to the stage of lactation and once each 
week the milk from each group was put into a separate 
can, the cows being groomed and milked in the usual 
manner by the regular attendants. A sample of milk 
was taken from each can for examination. Two guinea 
pigs were inoculated from each sample — one with the 
cream and one with the sediment. This was repeated each 
week for six weeks. Then the cows in the stable were 
again examined in the same way and, no symptoms indi- 
cating tuberculosis being found, samples of milk were 
collected and examined as before once a week for another 
period of six weeks. Altogether, 96 guinea pigs were 
inoculated. Thirty died of intercurrent disease and the 
other 66 were chloroformed two months after inoculation. 
A post-mortem examination was made of every animal, 
but in no instance were any lesions of tuberculosis found. 
One of the cows in the experiment had reacted to tuber- 
culin over 8 years before, one 7 years, two 6 years, two 4 
years, two 3 years, two 2 years, one 1 year and one 4 
months before. 

These observations show that non-clinical reactors 
play a minor role in the infection of market milk with 
tubercle bacilli, even when the virulence of the milk is 
tested by the delicate inoculation test. That there is a 
vast difference between the number of tubercle bacilli 
necessaiy to produce infection by the mouth and by in- 
oculation has been demonstrated by a number of investi- 
gators. Ostertag and others have shown that two and a 
half million times more material is required to infect an 
animal by feeding than by inoculation. Schroeder and 
Cotton found that milk which would produce tubercu- 
losis in guinea pigs when 5 c.c. was injected into the 
peritoneal cavity could be fed 30 days without producing 



90 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

the disease. Findel, Reichenbach and Alexander^'' found 
that at least 400,000,000 tubercle bacilli are necessary 
to produce infection when only a single dose is fed to 
guinea pigs and that 800,000 tubercle bacilli given fifty 
times by the mouth are not certain to produce infection. 
Ostermann^^ reports that milk containing 1000 bacilli 
per c.c. may be repeatedly ingested without effect. 
Fliigge and his co-workers also found that while a very 
few tubercle bacilli are sufficient to produce a severe 
tuberculosis when injected into a guinea pig, 200 are 
necessary when the bacilli are inhaled and 140,000,000 
when they are ingested. 

4. How can Contamination of Market Milk with 
Tubercle Bacilli he Prevented? — The information at 
hand shows that cows with tuberculosis of the udder are 
by far the greatest factors in infecting market milk with 
tubercle bacilli and that next in order are those with ap- 
parently healthy udders but showing clinical symptoms 
of the disease in other organs. Compared with these 
two classes, cows which present no evidence of tubercu- 
losis except a reaction to the tuberculin test are a rather 
insignificant source of contamination. 

The contamination of milk with tubercle bacilli can 
be most thoroughly and most certainly prevented by re- 
moving from the herds concerned in a milk supply the 
cows belonging to all three classes. This could only be 
accomplished by making a tuberculin test and ^physical 
examination and repeating them at certain intervals. A 

1^ Cited by Ostertag, Zeitschr. fiir Fleisch u. Milchhy., p. 
27, No. 2, vol. xxiii. 

^^ Cited by Klimmer, Osterreich. Wochenschr. fiir tierheilk. 
u. Tierzucht, No. 45, 1912. 



INFLUENCE OF DISEASE UPON MILK 91 

physical examination in addition to a tuberculin test is 
necessary because the tuberculin test alone will not detect 
all cases of tuberculosis. Ostertag, for instance, tested 
with tuberculin nine cows affected with udder tubercu- 
losis and two failed to- react. The adoption of such a 
plan, however, immediately upon the introduction of 
dairy inspection in districts in which tuberculosis is com- 
mon will meet with many practical difficulties. Few 
dairymen in such districts are able to bear the expense 
of disposing of non-clinical reactors as well as clinical 
cases and of replacing them with healthy cows, even 
with state assistance ; and the state would not have suffici- 
ent funds to render the assistance provided by present 
laws if such a plan was generally adopted. Difficulty 
would also be experienced in replacing the reacting cattle 
with animals free from tuberculosis, and this would in- 
crease with the number of herds included in the inspection. 
The opposition of the dairymen concerned would be 
very generally incurred and there would not exist that 
friendly cooperation between the inspector and dairy- 
man which is necessary to insure the most satisfactory 
results. A careful and thorough physical eojamination 
repeated at intervals is next in the order of effectiveness. 
By this method those cows can be discovered which are 
the most concerned in the contamination of milk with 
tubercle bacilli. Such an examination should include a 
careful inspection and palpation of the udder and supra- 
mammary lymph glands ; inspection of the milk in each 
quarter ; palpation of the other superficial lymph glands ; 
examination of the general condition of the animal; in- 
spection for nasal discharge; examination for cough; 
examination of the respiration ; auscultation of the lungs ; 
examination of the digestive tract, especially for chronic 



92 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

tympanites and diarrhoea, and inspection for vaginal 
discharge. In some cases it will also be necessary to take 
the temperature and pulse and to examine the lungs and 
pleura by percussion as well as auscultation, and in suspi- 
cious cases, when a definite decision cannot be made, it 
may be necessary to apply the tuberculin test to the ani- 
mal under examination or to collect sputum from the 
trachea or oesophagus, secretions from the vagina, scrap- 
ings from the rectum, and milk, and submit them to a 
microscopic examination and inoculation test (see p. 
275). In tuberculin-testing such animals, a large dose 
of tuberculin must be used, from two and one-half to five 
times the ordinary dose. When the microscopic examina- 
tion of material from an animal of this kind gives a nega- 
tive result it cannot be accepted as final, but guinea pigs 
must be inoculated. If death does not occur earlier, the 
guinea pigs must be held for two months after inoculation 
before they can be killed for post-mortem examination. 
Most owners would prefer to dispose of an ordinary cow 
on suspicion rather than feed it for this length of time 
and keep it isolated and not be permitted to use the milk 
without heating it. It is usually more satisfactory to 
apply the tuberculin test in such cases. Clinical cases 
of tuberculosis are usually unthrifty and are generally 
not good milkers and the owner can usually be convinced 
that such animals are unprofitable. Another reason for 
disposing of such cows, which will appeal to the owner, 
is that they are sources of infection for the other cattle 
in the herd. As a rule, the removal of animals of this 
kind, advice and assistance in securing healthy cows to 
replace them, and proper attention to the other features 
of dairy inspection will gain the confidence of the owner 
rather than his opposition, and after a system of inspec- 



INFLUENCE OF DISEASE UPON MILK 93 

tion of this character has been in operation for several 
years the tubercuHn test may be added with very httle 
objection. Fewer reactions will then be obtained and 
the reacting animals can be more readily replaced with 
non-tuberculous animals. 

When milk is produced especially for children's use, 
however, the greater susceptibility of children to tubercle 
bacilli of bovine origin must be taken into account, and 
the most thorough methods for protecting milk from con- 
tamination with tubercle bacilli should be applied. 
Children's milk should therefore be obtained only from 
herds which are tuberculin-tested at least once a year and 
which are subjected to a physical examination at least 
once each month. 

The efficiency of the clinical examination of dairy 
cows in preventing the contamination of a milk supply 
with tubercle bacilli as compared with the bacteriological 
examination of the milk for the presence of the bacilli 
is fairly presented in the following statement from the 
report of the British Commission on tuberculosis : *' The 
presence of tubercle bacilli in cow's milk can be dis- 
covered, though with some difficulty, if proper means be 
adopted," but " it is much easier to demonstrate with 
certainty by clinical examination that a cow is affected 
with tuberculosis and will in consequence perhaps pro- 
duce tuberculous milk." Furthermore, milk from a cow 
eliminating tubercle bacilli is not constantly infected. 
On certain days, the organisms may be absent entirely 
or present in only small numbers. A single examination 
may therefore give misleading results. 

The destruction of tubercle bacilli in milk by heat 
is considered in the chapter on pasteurization (page 203) . 



94 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Diagnosis of Tuberculosis of th€ Udder. — For a time after 
the disease has been established in the udder, the tubercles are 
not large enough to be discovered bj palpation and the milk 
retains its normal appearance, but during this initial stage 
of the disease symptoms are usually present in other organs 
which enable one to discover the presence of the disease by 
physical examination. In 119 cows affected with tuberculosis 
of the udder, Lungwitz ^^ found tuberculosis in other organs 
in every one. The observations of Rick and of Joest and 
Kracht, already quoted, show that the disease is usually gener- 
alized when the udder becomes infected. 

Tuberculosis of the udder runs a slow, insidious course. 
The perceptible changes in the udder which indicate its presence 
are firm nodules, which are neither hot nor painful, or a rather 
diffuse painless induration without local increase of tempera- 
ture, in one or more quarters. Later, abscesses may form and 
rupture (mixed infection) ; atrophy may also occur. The 
posterior quarters are most commonly affected. The supra- 
mammary lymph glands may be enlarged, while the udder is of 
normal appearance, but in these cases the udder is usually also 
infected. In rare cases, the disease runs an acute course, the 
udder showing the symptoms of acute inflammation. 

In contrast with what occurs in other forms of udder disease, 
the milk remains of normal appearance for eight to ten weeks, 
although it may be highly virulent. Finally, it becomes thin 
and transparent like water, assumes a yellowish color and con- 
tains small clots or flakes. When it is permitted to stand, a 
pus-like sediment is deposited with a yellow, transparent fluid 
resembling serum! above it. The acidity is reduced one-half 
(Raudnitz), or the reaction is even sometimes alkaline (Oster- 
tag). In advanced cases, the secretion of milk ceases and only 
a purulent fluid in moderate amount can be obtained from the 
affected quarter. 

Diagnosis of Open Tuberculosis. — (a) Pulmonary Tubercu- 
losis. — The most characteristic s3anptom is a chronic cough, at 

^^ Leblanc, Diseases of Mammary Gland (Nunn's transla- 
tion). 



INFLUENCE OF DISEASE UPON MILK 95 

first vigorous, later weak. The respiration is often unchanged, 
but in advanced cases it is usually rapid and labored. Sometimes 
there is a purulent nasal discharge. Percussion does not 
usually give much information ; on auscultation increased vesicu- 
lar murmur, rales, and indefinite sounds may be detected. These 
symptoms are usually accompanied by anaemia, unthriftiness, 
emaciation, dull and sunken eyes, variable or poor appetite, 
diarrhoea, repeated bloating after meals, or distention of the ju- 
gular vein. In advanced cases the pulse is accelerated and soft. 

(6) Intestinal Tuberculosis. — The symptoms of intestinal 
tuberculosis are not characteristic. Repeated attacks of colic 
and constipation alternating with diarrhoea are the most sus- 
picious. The intestinal discharges may be quite fluid and 
frequently contain mucus and pus, sometimes blood. The diges- 
tive disturbances which are nearly always present in advanced 
tuberculosis are usually due to the involvement of the intestines, 
but on the other hand, they may be entirely absent when the 
intestines are tuberculous. 

(c) Tuberculosis of the Uterus. — A turbid, mucous or muco- 
purulent discharge, yellowish or rather ichorous and of foul 
odor, is a constant symptom of tuberculosis of the uterus. Frag- 
ments of caseous material or streaks of blood are sometimes 
present. The cow is sterile and frequently in heat. On rectal 
examination the sacral lymph-glands may be found enlarged or 
the horns of the uterus hard and nodular. 

When the mucous membrane of the vagina or vulva is tuber- 
culous, ulcers or nodules are present, together with a similar 
discharge. 

Enlargement of the superficial lymph glands is an important 
symptom. 

While these symptoms in themselves are not sufficient to 
justify a positive diagnosis of tuberculosis, nevertheless when 
they are presented by an animal in a herd in which tuberculosis 
is known to exist, and when other possible causes for them can 
be excluded, an error will not often be made if the animal is 
regarded as tuberculous. In doubtful cases the tuberculin test 
can be applied or a microscopic examination or an inoculation 
test made. 



96 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

APHTHOUS FEVER OR FOOT AND MOUTH DISEASE 

In the milder forms of foot and mouth disease the 
milk secretion may not be affected, but in the more severe 
cases the milk flow is reduced one-half and the milk is con- 
siderably changed in composition and appearance. The 
alterations are similar to those observed in inflammation 
of the udder. The albmnin, globulin and salts are in- 
creased in quantity, while the sugar, casein, and usually 
the fat are decreased, although sometimes the fat is in- 
creased. The milk becomes thin, and after it stands 
for a while a layer of slimy, dirty cream forms at the 
top of the fluid and considerable sediment is deposited 
at the bottom of the vessel. When examined microscopic- 
ally, the sediment is found to be rich in cells — epithelial 
cells, leucocytes, and red-blood cells. The milk coagu- 
lates when boiled, reacts positively to the alcohol test and 
contains a large amount of catalase. 

Nocard has shown that the milk of affected cows does 
not contain the virus of foot and mouth disease when it 
is drawn from the udder in a manner which pre- 
vents external contamination. But when vesicles or 
ulcers are present on the teats or udder it is not possible 
to draw milk in the ordinary way without it becoming 
contaminated with the virus. Merely a trace of the serum 
from the vesicles is suflicient to render 50 to 100 quarts 
of milk infectious. Practical experience indicates that 
the milk of affected cows is frequently infectious. Fur- 
thermore, the extraordinary facility with which the virus 
is disseminated makes it extremely probable that all of 
the milk of a herd in which the disease exists may be 
infected secondarily. 

The disease may be transmitted to man through milk, 



INFLUENCE OF DISEASE UPON MILK 97 

and also to cattle and swine. It may also be transmitted 
by butter and cheese. Man may be mildly or severely 
affected; in some instances, the disease has terminated 
fatally. The symptoms are fever, weakness, conjuncti- 
vitis, nausea, vomiting, and diarrhoea, with formation of 
vesicles on the mucous membrane of the lips, mouth or 
nose, and on the ears, fingers or other places on the body; 
sometimes the skin is red and the joints painful. 

The sale of milk from herds in which foot and mouth 
disease exists should not be permitted, unless it is heated 
sufficiently to destroy the virus and is not changed in 
appearance. The virus is not very resistant. A tempera- 
tureof50°C. (122° F.) for 15 minutes; 70° C. (168° F.) 
for 10 minutes; or 85° C. (185° F.) momentarily will 
destroy it (Ernst). 

COWPOX 

Cowpox is closely related to variola or smallpox of 
man. Before vaccination was introduced, when smallpox 
frequently became epidemic, it is very probable that cow- 
pox often originated from this source. Vaccinia of man is 
also transmissible to cattle and many instances are on 
record in which cows have been infected by vaccinated 
persons. Infection takes place during milking as a rule, 
the contagion being rubbed into the skin of the teat by 
the hands of the milker. The disease is therefore most 
commonly seen in cows in milk. It usually begins with a 
rise of temperature, but this may pass unnoticed unless 
it is accompanied by dullness and loss of appetite, as is 
sometimes the case. The teats and neighboring parts of 
the udder become swollen, hot, and painful. In two or 
three days, papules appear, which may be as large as a 
pea and which are surrounded by a red area. On the 
7 



98 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

udder they are round ; on the teats oblong, with the great- 
est diameter parallel with the length of the teat. In a 
day or two they change into vesicles of a bluish-white 
or yellowish- white color. The vesicles ripen into pustules 
in eight or ten days and a depression or umbilication 
appears in the top, after which they ruptui'e and leave 
an ulcer, or dry and heal under a scab. They may be 
ruptured during milking before they are ripe. 

The milk may become thin, bluish, and of lighter 
specific gravity than normal; it may be nauseating and 
may coagulate very readily. The acidity may be below 
normal. These changes, however, do not always occur. 
When the disease is complicated with parenchymatous 
mastitis, as sometimes happens, then the milk undergoes 
the pronounced changes which occur in the latter con- 
dition (see page 109). 

Cowpox is transmitted from cow to cow by the milker 
and by infected bedding, fodder, and stalls. The disease 
is also transmissible from the cow to man through milk. 
There is no proof that the virus is excreted through the 
udder, but as the pox are located on the teats and the 
adjacent parts of the udder it is practically impossible 
to draw the milk without the virus contained in the ves- 
icles and pustules getting into it. Stern saw cowpox 
transmitted to a large number of children by milk from 
a dairy in which the disease was enzootic. The children 
were affected with an eruption on the face which healed 
under a scab. Not many such observations have been 
recorded, however. The reason for this is that the general 
custom of vaccinating against smallpox has rendered 
most persons immune to the disease. The transmission 
of the disease to the milkers by direct infection of wounds 
on the hands or fingers has been more frequently ob- 



INFLUENCE OF DISEASE UPON MILK 99 

served; in some cases the face has been affected in this 
way. 

Milk from cows affected with cowpox should not be 
used for food. When the disease is enzootic, the healthy 
and diseased cows should be separated and separate 
milkers provided for each class. This is especially im- 
portant when the milk is to be used by children. The 
virus of cowpox is destroyed by a temperature of 48° C. 
(119° F.). Milk from infected animals which has not 
undergone any physical change and milk which has been 
exposed to infection may be rendered safe by heating to 
this temperature. 

False Cowpox. — Cowpox should not be confused with 
a condition more commonly affecting the udder which 
is known as false cowpox. In this condition, small nodu- 
lar swellings which may be as large as a pea appear on 
the teats and neighboring parts of the udder, rupture in 
a few days, and then heal under a scab. The teats are 
not hot, swollen or tender and there is no red area around 
the nodules, as in true cowpox; fever is also absent. The 
condition is supposed to be caused by the ordinary pyo- 
genic cocci, which are rubbed into the skin during milk- 
ing or enter through wounds. Cows with teats covered 
with a fine skin seem to be most susceptible. The condition 
may be transmitted from cow to cow by the hands of 
the milker, but is not transmissible to man. The milk is 
not affected except in so far as it may be contaminated 
with purulent matter from the ruptured nodules. There 
is only a small quantity of this material and the con- 
tamination from this source therefore can only be very 
slight. 

Furunculosis of the Udder is sometimes called cowpox 
by dairymen. This condition usually occurs sporadically, 



100 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

but it is occasionally enzootic, especially when musty 
or mouldy straw is used for bedding. It is most fre- 
quently seen in fresh cows, after they have been put on 
full feed, and it is probably for this reason that the fu- 
runcles are spoken of as feed boils. Firm, painful, nodu- 
lar swellings, varying in size from a pea to a walnut, 
appear in the subcutaneous tissue of the udder. In 
seven or eight days a dark area of puriform softening 
develops in the centre of each individual swelling, which 
subsequently ruptures at this point and discharges its 
contents of pus mixed with shreds of tissue. This dark 
patch, or the scab of dried blood which subsequently 
forms at the point of rupture, has given the process the 
popular name of blach scab in some sections. The milk 
secretion is not affected, but the milk may be contami- 
nated secondarily with the purulent discharge. 

ANTHRAX 

The question of using the milk from a cow affected 
with anthrax does not often arise in practice because, 
as a rule, the milk secretion ceases suddenly with the onset 
of the fever, while in those cases in which it continues 
it is reduced to a small quantity and is very much changed 
in appearance. It is more yellowish than normal, slimy, 
sometimes bloody, with a bitter taste, and after standing 
undisturbed for a few hours separates into a layer of cream 
and of serum. Anthrax bacilli are excreted through the 
udder only in the advanced stages of the disease, after they 
have invaded the blood stream and when the udder is 
affected. But the chances of milk becoming infected 
secondarily are very great. The bloody discharges and 
the manure from infected animals contain the anthrax 



INFLUENCE OF DISEASE UPON MILK 101 

bacilli and their spores, and the spores may also be 
present in the dust of the stable and in the dust of straw 
and hay from infected fields. The organisms may gain 
access not only to the milk of the affected cow, but also 
to the milk of other cows in the stable. Anthrax bacilli 
and spores entering milk in this way may multiply 
rapidly, as milk is an excellent culture medium for this 
organism. While the bacilli are digested by the gastric 
juice, the spores are not affected and in disturbances of 
digestion the bacilli may also escape destruction. Ernst 
mentions a typhoid fever patient who developed intestinal 
anthrax after drinking milk from a cow with a malignant 
pustule on the udder. 

All milk from a herd in which anthrax is present 
must therefore be regarded as dangerous to man until 
proper precautions are taken to prevent the secondary 
infection of the milk from the cows which are not diseased. 
Diseased and dead animals should be at once removed 
from the stable, which should be thoroughly cleaned and 
disinfected. McFadyean recommends that the tempera- 
ture of every exposed cow be taken each day before milk- 
ing for seven to ten days, and that all those showing a rise 
of temperature be treated as suspicious cases and taken 
out of the stable, the milk not being used. 

RABIES 

Cattle are usually infected with rabies by being 
bitten by a rabid dog. Frequently several animals in a 
herd are infected at the same time. While the virus of 
rabies is to be found in its purest and most concentrated 
form in the central nervous system, it is also present in 
the milk of affected animals as well as in the secretions 



102 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

of the salivary and lachi-ymal glands and pancreas. 
Numerous feeding experiments with milk and other sub- 
stances from rabid animals show that the virus is not 
absorbed, and that the disease is not produced, when the 
mucous membrane of the digestive tract is intact and the 
digestive functions are acting normally. In the upper 
part of the digestive tract, stratified squamous epithelium 
acts as a barrier to the entrance of the virus into the blood 
stream and when it reaches the stomach it is digested by 
the gastric juice. But when wounds are present in the 
mucous membrane of the lips, mouth or throat, or when 
the secretion of gastric juice is disturbed, the ingestion 
of milk containing the virus of rabies may produce the 
disease. Milk from cows affected with rabies must there- 
fore be regarded as dangerous. Whether the milk of 
infected cows contains the virus before symptoms of the 
disease appear, as is the case with the saliva of dogs, is 
not known. Until this question is determined it will be 
advisable not to use the milk of a cow which has been 
bitten by a rabid dog until it is determined that infection 
did not occur. 

ACTINOMYCOSIS 

Actinomycosis usually affects the maxillae, tongue or 
other parts about the head, but it sometimes occurs in 
the udder, also in the lungs and other internal organs. 
When present in the udder it is usually of primary 
origin, i.e., the infection enters through the teat canal. 
Actinomycosis of the udder is generally indicated by the 
presence of one or several fii'm nodules of the size of a 
bean up to a hen's egg in one or more quarters of the 
organ. These nodules consist of a thick wall of connec- 
tive tissue surrounding a purulent centre in which the 
actinomyces may be seen in the form of sulphur-yellow 



INFLUENCE OF DISEASE UPON MILK 103 

gi'anules. They may rupture internally or externally 
and discharge pus containing the fungi. The milk cis- 
tern may be filled with the nodules. Sometimes the dis- 
ease appears in the udder in a miliary form ; the affected 
quarters are enlarged, hard and somewhat nodular, and 
on section numerous very small nodules of granulation 
tissue with softened purulent centres are found dissemi- 
nated through the gland tissue. Similar nodules may be 
found on the mucous membrane of the larger canals and 
cistern. Numerous actinomyces are found in the soft- 
ened centre of the nodules. As a rule, actinomycosis 
of the udder has not been recognized until after the 
slaughter of the affected animal, consequently nothing 
definite is known regarding the appearance of the milk 
in this condition. Up to this time, actinomyces have not 
been demonstrated in milk, but they are no doubt ex- 
creted with the milk when the actinomycotic nodules rup- 
ture into an alveolus or duct of the udder. The milk 
may be infected secondarily when an actinomycotic 
nodule in the udder ruptures externally or when an actin- 
omycotic tumor in the maxilla or adjacent parts opens. 
In such cases the discharge contains not only actinomyces 
but also bacteria, particularly the pyogenic organisms, 
and these, too, may gain access to the milk. 

There is no record of the transmission of actinomy- 
cosis to man through milk. Tliis may be due in part to 
the slow development of the disease, as in the case of 
tuberculosis. Infection with actinomyces may occur in 
man, as it does in cattle, through the food, especially 
when wounds exist in the mouth or other anterior parts 
of the digestive tract. Since there is a possibility of the 
transmission of this disease by milk, it is advisable to 
exclude from dairies all cows with actinomycosis of the 



104 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

udder or with open, discharging actinomycotic tumors. 
Milk from cows in the latter condition is further objec- 
tionable because it may contain pus and pyogenic or- 
ganisms, and, in advanced cases, for the additional reason 
that the general condition is affected, the animal becom- 
ing emaciated, weak and dull. 

MILK SICKNESS OR TREMBLES 

Cattle and horses when pastured on certain lands in 
circumscribed areas in the United States develop a dis- 
ease known as milk sickness or trembles. Its etiology 
has been the subject of much speculation and investiga- 
tion. In 1907 Jordan and Harris isolated in pure culture 
from the blood and organs of animals dead of the disease 
a spore-forming bacillus with which they succeeded in 
reproducing the disease in experimental animals. They 
have given this organism the name of Bacillus lactimorbi. 
The principal s5Tnptoms of the disease are violent trem- 
bling and great restlessness, followed by paralysis. The 
animal may fall and die suddenly, but usually it lies sev- 
eral days in a paralyzed condition. The disease is trans- 
mitted to man through the milk, butter, and meat from 
aff'ected animals. The symptoms in man are severe 
vomiting, difficult breathing, subnormal temperature, 
paralysis, and death. 

II. Diseases of Cattle which may Render Milk 
Harmful to Man. 

INFLAMMATION OF THE UDDER— MASTITIS 

Cows are very frequently aff*ected with mastitis, a 
disease of great economic as well as hygienic importance. 
There are three forms of the disease : ( 1 ) Catarrhal mas- 
titis, which may be either mucous or purulent, and which 



INFLUENCE OF DISEASE UPON MILK 105 

runs a subacute or chronic course; (2) parenchymatous 
mastitis, which is pm-ulent and acute, and which is some- 
times accompanied by abscess formation and gangrene, 
and (3) interstitial mastitis, which may be a simple in- 
flanmiation or a phlegmonous condition. The three forms 
diiFer in the type of the inflammation (acute or chronic) , 
the part of the udder tissue affected, the effect upon the 
milk secretion, and in the character of the bacteria con- 
cerned. One form may be associated with another. The 
disease is commonly called " garget " by dairymen and 
farmers. 

1. Catarrhal Mastitis. — From a hygienic standpoint, 
catarrhal mastitis is of greatest importance because it 
occurs more frequently than the other forms and also 
because the milk may contain the causative bacteria be- 
fore clinical symptoms or marked changes in the milk 
are apparent and for a time after they have disappeared. 
This latter circumstance has been the inspiration of 
numerous efforts to discover a method of examining milk 
by which this disease could be detected in its incipiency. 

CataiThal mastitis is a mucous or purulent catarrh 
of the mucous membrane of the teat canal, milk cistern, 
and large milk ducts. It is frequently accompanied or 
followed by a productive inflammation of the submucous 
and interstitial connective tissue, in which case it often 
terminates in atrophy of the gland tissue and loss of 
function. It is usually caused by streptococci of varying 
degrees of virulence; sometimes, but not often, mucous 
catarrh occurs without the intervention of bacteria from 
the effects of cold or overfeeding. The symptoms are 
never pronounced. The history of the cow is of great 
assistance in detecting incipient cases, although it is 
sometimes difficult to obtain. A statement that the cow 



106 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

" milks hard," Le„ that there is difficulty in expressing 
the milk through the teat canal, or that the milk is not 
"let down " or is " drawn up," or that the cow has recently 
developed a tendency to kick during milking, should ex- 
cite suspicion of the presence of the disease. The first 
condition is due to obstruction of the teat canal by swell- 
ing of the mucous membrane or by dried secretion; the 
others occur because milking is painful. Among the 
first noticeable symptoms of the disease are changes in 
the milk stream expressed from the teat. This may be 
split, deflected from the proper direction, or it may not 
be cut off promptly and may therefore smear the end of 
the teat — all indications of catarrh of the mucous mem- 
brane of the teat canal. In such cases small yellow crusts 
may be found covering the opening of the teat canal, but 
crusts of dried milk may also be present at this point when 
the sphincter of the teat canal does not close properly. 
When pressure is exerted upon the lower end of the teat, 
a drop of pus or mucus may be squeezed out of the teat 
canal or the thickened mucous membrane may project 
through the opening. Later, the mucous membrane of 
the cistern may become thickened, in which case a cord 
about as thick as a lead pencil is felt running through the 
middle of the teat when the teat is rolled between the 
thmnb and fingers. Flat, disc-shaped thickenings about 
the size of a quarter dollar and nodular indurations may 
be present in the upper limits of the cistern when the 
mucous membrane of the lower end of the large milk 
ducts is thickened. Growths upon the wall of the cistern 
or teat canal (" spider in the teat") may also be dis- 
covered by palpation. The induration usually extends 
slowly into the interstitial tissue, generally from the teat 



INFLUENCE OF DISEASE UPON MILK 107 

upward, producing a hard firm area ("cake," "caked 
udder," " cold garget "), which may eventually involve 
the entire quarter. The newly formed connective tissue 
subsequently contracts and causes atrophy of the gland 
tissue and loss of function. 

In the early stages of the disease, and also throughout 
mild cases of mucous catarrh, the milk does not show any 
marked change at the time it is drawn from the udder. 
Very often it contains small flakes, some of which may 
be as small as a pin-head; they may be present only in 
the first milk drawn, but sometimes they do not appear 
until the middle or at the end of the milking. After the 
milk stands for a time, or is centrifugalized, a grayish- 
yellow sediment is deposited and a dirty-gray, clumpy 
or granular cream layer is formed. In severe cases of 
mucous catarrh, the secretion becomes slimy and viscid. 
In purulent catarrh, the secretion of milk djecreases 
while the pus cells and fibrin increase and the fluid ob- 
tained from the affected quarter gradually changes to 
a thick, yellowish, purulent exudate or to a yellowish 
serum containing clumps of pus and fibrin. Frequently, 
the exudation ceases entirely and the milk secretion does 
not return until the next lactation or not at all. The 
chemical composition of the milk is only slightly changed 
at the beginning of the disease, the lactose being de- 
creased and the mineral salts, especially the sodium chlo- 
ride, increased, while the other constituents are present 
in the usual amount. Later, there is a greater decrease 
in the lactose, the casein is also below normal, and the 
fat is usually decreased, while the albumin, globulin, and 
mineral salts are increased. Fibrin is also present. The 
reaction of the milk is usually, but not always, alkaline. 
The taste is salty or bitter. Cells are present in large 



108 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

numbers in the sediment and cream, especially the poly- 
morphonuclear leucocytes in purulent catarrh. The 
catalase content is increased. Coagulation occurs when 
the alcohol or the boiling test (see pages 284, 285) is 
applied. 

On account of the difficulty of detecting catarrhal 
mastitis in its early stages, the determination of the leuco- 
cytic content of samples of market milk has sometimes 
been relied on to discover the presence of the disease. It 
has been demonstrated that cases of catarrhal mastitis 
may be detected by this method but we have no means of 
knowing how many of such cases escape discovery ; there 
is reason to believe that many are overlooked. The ex- 
amination of samples of milk from individual cows by 
means of the catalase test is the most efficient method of 
detecting the disease (see page 287) . When numerous 
very small, punctiform, brownish colonies appear in the 
plates prepared for determining the number of bacteria in 
milk and these are found upon microscopic examination to 
consist of streptococci in long chains, an examination of 
the herd will usually discover the presence of one or more 
cases of catarrhal mastitis. 

A special form of purulent catarrhal mastitis which 
leads to multiple abscess formation is caused by the Bacil- 
lus pyogenes. The secretion has a foul odor. The disease 
occurs most commonly in " dry " cows, but is usually not 
discovered until they become " fresh." 

2. Parenchymatous Mastitis. — The detection of this 
form of mastitis offers no difficulties to the dairy inspec- 
tor. It is attended with an immediate and pronounced 
swelling of the aff'ected portion of the udder and the milk 
at once presents marked changes. As the name indicates, 
it is an inflammation of the alveoli and small tubules of 



INFLUENCE OF DISEASE UPON MILK 109 

the udder and is usually caused by the Bacillus phleg- 
masia uberis or other varieties of colon bacilli, sometimes 
by organisms of the paracolon or paratyphus group, the 
enteriditis bacillus or by staphylococci. Septicaemia may 
develop in the course of the disease. Severe cases may 
terminate in gangrenous mastitis. In the beginning of 
the disease, and throughout mild cases, a turbid fluid 
resembling whey in appearance and containing flakes of 
casein, is obtained from the affected quarter. Later, in 
cases of medium degree, the fluid resembles serum and 
contains clots of fibrin. In the more severe cases, the 
secretion is discolored with blood. In gangrenous mas- 
titis, a small amount of bloody-serous, dark, foul-smelling 
fluid, which contains gas bubbles, may be obtained from 
the affected quarter. The chemical changes which occur 
in the milk in parenchymatous mastitis are similar to those 
which take place in catarrhal mastitis. There is a de- 
crease in the lactose, which is sometimes entirely absent ; 
the fat is usually decreased, although sometimes it is in- 
creased ; the casein is decreased, while the albumin, glob- 
ulin, and salts, especially sodium chloride, are increased. 
The taste is salty or bitter. There is an increase in the 
content of catalase and coagulation takes place when the 
alcohol or boiling test is applied. 

3. Interstitial Mastitis. — The simple, traumatic form 
of interstitial mastitis, in which the inflammatory process 
is limited in extent and rather mild, has no important 
effect upon the milk secretion, but when the disease is 
due to the entrance of bacteria through fissures or 
wounds, as is most frequently the case, a phlegmonous 
inflammation occurs in the subcutaneous or interstitial 
connective tissue which is accompanied by a rise of the 
bod}^ temperature, sometimes to 107° F., and other sjTup- 



110 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

toms of constitutional disturbance. There is then more 
or less extensive and painful swelling of the affected 
quarter which begins at the teats and extends upward. 
The milk secretion is somewhat reduced in quantity in 
the beginning of the disease, but is otherwise unchanged. 
Later, the secretion from the affected quarter is dimin- 
ished ; the fat is decreased and the milk has a pale, watery 
appearance. The inflammation may extend into the 
gland tissue, in which case the milk will undergo the same 
changes as in parenchymatous mastitis. 

Harmful Properties of Mastitis Milk. — In mastitis 
the secretion from the udder nearly always contains bac- 
teria which may be harmful to man. In the catarrhal 
form streptococci are usually present, sometimes staphy- 
lococci or the Bacillus pyogenes. In the parenchymatous 
form bacteria of the colon gi-oup are usually present, 
sometimes bacilli of the paratyphus or paracolon group, 
the enteriditis bacillus, or staphylococci. In catarrhal 
mastitis the bacteria may be present when the milk is of 
normal appearance and before clinical symptoms appear 
and also after the clinical symptoms have subsided and 
the milk has again become normal in appearance. Bac- 
teria not only occur in the secretion from the affected 
quarter but they may also be present in the milk from the 
other quarters. The skin of the teats and udder is con- 
taminated by the secretion from the diseased quarter and 
some of this infected material can easily fall into the milk 
pail during the drawing of milk from the other quarters. 
Secondary infection of the milk is also likely to occur 
when the secretion from the diseased quarter is milked 
onto the floor, as is frequently done. The mastitis bac- 
teria find an excellent culture media in milk and rapidly 
multiply when the milk is kept at room temperatm'e. 



INFLUENCE OF DISEASE UPON MILK 111 

Considering the frequency of the catarrhal and paren- 
chymatous forms of mastitis in dairy cows, cases of 
illness in man resulting from the ingestion of milk from 
cows affected with this disease have not been reported as 
often as would be expected. There are several reasons 
for this. The milk from a diseased cow may be diluted 
with milk from cows in normal condition to such an extent 
as to render the mixed milk harmless. Furthermore, 
some of the mastitis bacteria have a relatively low 
virulence for man. Finally, it rarely happens that the 
physician is able to establish the connection between the 
disease in his patient and the cow aifected with mastitis, 
even when milk from the latter is the cause of the disease. 
Nevertheless, there are on record numerous cases of ill- 
ness in man caused by the ingestion of milk from cows 
affected with mastitis, the symptoms in these cases being 
nausea, vomiting, and diarrhoea, sometimes associated 
with fever, faintness, languor, and cramps in the legs. In 
two instances the milk which was the cause of the disease 
had been boiled. It is not known whether the illness in 
these cases was due to a heat-resisting toxin or to bacteria 
which survived the heat because of the protection fur- 
nished by the membrane which forms on the surface of 
milk when it is heated. 

Numerous epidemics of septic sore throat have been 
reported in which the infection was transmitted by milk. 
In some of these epidemics, cows affected with strepto- 
coccic mastitis were found to be the source of the infec- 
tion, but in the other outbreaks the circumstances seemed 
to point to the infection of the milk by dairy workers suf- 
fering from the disease. To account for the persistence of 
streptococci for several days in the milk supplies involved 
in the second group of epidemics, the theory has been 



112 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

advanced by Theobald Smith that the offending organ- 
isms were introduced into the udder of some of the cows 
by infected milkers, multiplied there without producing 
any changes in the organ or in the milk, and were elimi- 
nated in the milk in large numbers at each milking. In 
two of the epidemics in the United States (Chicago 
1911, Baltimore 1912) , the milk which spread the disease 
had been subjected to a pasteurizing process. Rosenau 
observed that when the Streptococcus pyogenes is grown 
in raw milk it is modified to correspond with the strepto- 
coccus of epidemic sore throat. 

Milk from cows affected with catarrhal and paren- 
chymatous mastitis is also objectionable because the pus 
which it contains often gives it an unpleasant taste and 
frequently causes it to putrefy and to curdle quickly. 
The pus itself may be harmful to children, even if no 
bacteria are present. The greatest harm, however, is 
done by the bacteria. In the phlegmonous form of inter- 
stitial mastitis the presence of fever and other constitu- 
tional disturbances renders the milk unsuitable for food ; 
there is also the possibility that the parenchyma of the 
udder may at any time become affected and the causative 
bacteria would then be eliminated in the milk. 

Therefore, when a cow is affected with mastitis, the 
milk should not be used for food and, if possible, the cow 
should be removed from the milk stable until the udder 
returns to the normal condition. Cows affected with 
infectious streptococcic, septic, or gangrenous mastitis 
should always be isolated. When infectious streptococcic 
mastitis is present in a herd it may be necessary to pro- 
hibit the use of any of the milk for food unless it is 
boiled or pasteurized, but even then such milk should 
not be used for children. 



INFLUENCE OF DISEASE UPON MILK 113 

BLOOD IN MILK 

A mixture of blood with the milk may occur as a 
result of traumatisms of the udder, such as kicking, hook- 
ing or treading, which cause hemorrhages or blood infil- 
trations into the udder tissue. The pulling or dragging 
to which a greatly distended udder is subjected when the 
cow walks may cause a tearing of the udder tissue which 
will permit the mixing of blood with the milk. When 
large blood vessels have been injured the milk is colored 
diffusely red. But when small vessels are torn or rup- 
tured, which is more often the case, only small streaks of 
blood are observed which disappear when the milk is 
shaken and do not discolor it. When such milk is centri- 
f ugalized, the sediment shows a red color which, on micro- 
scopic examination, is found to be due to the presence 
of red-blood cells. Blood is observed in the colostrum 
or milk during the first week following parturition in 
those cases in which the udder is intensely hypertemic, 
resulting in a diapedesis of red-blood cells. 

(EDEMA OF THE UDDER 

Sometimes, especially in heifers with the first calf, 
the udder becomes very much swollen and oedematous 
shortly before parturition. The swelling is not hot, nor 
is it painful unless the skin is intensely stretched; it 
disappears a few days after parturition. Usually, no 
essential changes are observed in the milk. It is probable 
that some of the serous transudate is mixed with the 
milk, but nothing definite is known on this point. Some- 
times the milk contains blood. Generally, the oedema 
has disappeared by the time the colostral stage is passed. 
8 



114 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

INDIGESTION 

When the digestive functions of the dairy cow are 
distm-bed, as in gastro-intestinal catarrh, there is not 
only a decrease in the quantity of milk secreted, but quite 
frequently the milk has a bitter or salty taste and coagu- 
lates prematurely ( six to eight hours after milking) . It 
contains less fat than normal milk and sometimes appears 
thinner and of a yellow color. Milk from cows in this 
condition may possess irritant properties and when in- 
gested unmixed with the milk of other cows may produce 
diarrhoea, especially in children. 

The milk may undergo similar changes in other in- 
ternal diseases which do not directly involve the udder. 

Spoiled Feed. — The milk of cows fed on mouldy, 
fermented, or putrefied feed has produced diarrhoea in 
persons ingesting it. This effect has been attributed to 
the elimination in the milk of abnormal substances con- 
tained in such feeds, but it is possible that the organisms 
causing the changes in the feed may have gained access 
to the milk during milking and caused changes in the milk 
itself which brought on the diarrhoea. 

SEPTIC OR HEMORRHAGIC ENTERITIS 
This disease consists of a severe or bloody dian-hoea 
associated with a high temperature and other constitu- 
tional disturbances. It may occur sporadically or en- 
zootically, especially among young cattle. According to 
Jensen, it is caused by bacteria of the paracolon group 
which circulate in the blood and which are also present 
in large numbers in the fecal discharges. Secondary in- 
fection of the milk during milking is almost certain to 
occur since the udder, thighs, and flanks of the diseased 
animal will be soiled by the fecal matter. The bacteria. 



INFLUENCE OF DISEASE UPON MILK 115 

having entered the blood stream, may also be excreted 
in the milk when hemorrhages have occurred in the udder 
tissue. Two instances are reported in which milk from 
cows affected with this disease has produced disease in 
man. One individual was affected with diarrhoea, weak- 
ness, and headache, while the other exhibited symptoms 
resembling typhoid fever. Cows affected with a severe 
or bloody diarrhoea or with a diarrhoea associated with 
fever should be removed from the milk stable, since they 
are likely to infect not only their own milk but also the 
milk of other cows with pathogenic bacteria. The stable 
should be cleaned and disinfected. 

SEPTIC METRITIS 

In acute septic metritis, the milk secretion usually 
ceases with the sudden onset of the fever and the animal 
generally dies in a few days, so that the question of using 
the milk does not often have to be considered. In the 
less acute cases, a large amount of chocolate-colored fluid, 
which is frequently putrid, is excreted from the uterus 
and soils the tail, inner surface of the thighs, and udder, 
as well as the bedding, stall, and suroundings. This fluid 
may contain staphylococci, streptococci, bacilli of the 
colon and paratyphus groups, and putrefactive bacteria. 
These organisms may enter the milk during milking. 
The milk of such animals usually gives a positive reac- 
tion to the alcohol test, indicating that some of the prod- 
ucts of the disease are absorbed from the uterus and 
eliminated through the udder. The foul odor of the 
uterine discharges and the odor of antiseptics which may 
be used in the treatment of such cows will be absorbed 
by the milk. While no cases of disease in man from the 
use of milk from cows affected with septic metritis have 



116 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

been reported, there is no doubt that the milk is injurious 
to health because numerous cases of meat poisoning are 
on record from the use of meat from cows slaughtered 
while suffering from this condition. Cows affected with 
septic metritis should therefore be removed from the milk 
stable and the milk should not be used for food. 

RETAINED PLACENTA 
Following retention of the placenta, there is a dis- 
charge from the uterus which frequently contains par- 
ticles of the fetal membranes and cotyledons which are 
undergoing putrefaction, also pus, pyogenic organisms, 
and putrefactive bacteria. The tail, thighs, and udder 
become soiled with the discharges and the milk may be 
contaminated during milking. In cases where the milk 
has been centrifugalized and the sediment examined micro- 
scopically, large numbers of staphylococci and diplococci 
have been found. The milk will also give a positive re- 
action to the alcohol test, indicating that the secretion is 
not normal. Milk from cows with a purulent or putrid 
vaginal discharge should not be used for food purposes. 
Such cows should not be placed in the milk stable 
until the condition disappears, as there is a possibility of 
the discharge contaminating the milk of the other cows. 

INFECTIOUS ABORTION 
The milk of cows which have aborted contains the 
Bacillus abortus Bang very frequently, in some cases for 
months after the abortion. Immediately before and 
for several weeks after abortion, the bacillus is also elimi- 
nated through the vagina and may infect the milk second- 
arily. When the placenta is retained, the vaginal dis- 
charge also contains pyogenic and putrefactive organ- 



INFLUENCE OF DISEASE UPON MILK 117 

isms. At the time of abortion the udder secretion fre- 
quently assumes the characteristics of colostrum. 

When injected into guinea pigs or fed to them, milk 
containing the abortion bacillus produces proliferative 
changes similar to those caused by the tubercle bacillus. 
The organism is also pathogenic for animals of several 
other species. This widespread pathogenicity and its 
frequent occurrence in milk suggested the desirability 
of investigations to determine if the organism was con- 
cerned in the sclerotic changes occurring in the organs 
and tissues of man and the domestic animals. Mohler 
and Traum inoculated guinea pigs with material from 
twenty-eight tonsils and adenoids from milk-consuming 
children. The material from two of the tonsils produced 
lesions in three guinea pigs, but the Bacillus abortus was 
recovered only from the lesions in one of these animals. 
Whether the organism was actually responsible for the 
change in the tonsil or whether it merely happened to 
be lodged on the surface could not be determined. 
Schroeder also made a number of similar tests, all with 
negative results. Mohler tested the blood serum of 
twenty-five persons with the complement fixation and 
agglutination tests and obtained negative results in all 
cases, while Larsen and Sedgwick, in applying the com- 
plement fixation test to the blood serum from 425 chil- 
dren, obtained 73 positive reactions (17 per cent.). 
Ramsey tested the blood of 116 children in the same 
manner, but the reaction was positive in only seven cases. 
Nicholl and Pratt obtained positive reactions with the 
agglutination test on the blood serum of several children. 
No definite statement can be made as to whether the anti- 



118 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

bodies responsible for these positive reactions were 
present because the individuals from which the blood 
samples were obtained had actually passed through some 
form of disease due to the abortion bacillus or whether 
they were the results of a passive immunity due to the 
ingestion of milk containing the bacillus or its antibodies. 
But it has been demonstrated in a number of experiments 
that after the ingestion of an organism in large num- 
bers the specific antilodies may be present in the blood 
without the organism producing disease, and there is 
some reason to believe that antibodies contained in the 
milk may be absorbed by the blood from the intestinal 
canal of children (see page 43). However, there is 
no definite information that abortion bacilli in milk have 
any injurious effect upon the health of individuals in- 
gesting such milk. 

OTHER DISEASES 

Any disease of the dairy cow attended with a con- 
siderable disturbance of the general condition usually 
causes a decrease or a complete cessation of the milk 
secretion. Although the milk is generally of normal 
appearance when secretion continues in such cases, it 
frequently contains an increased amount of mineral salts, 
has a salty taste and coagulates prematurely. While it 
is not known that milk of this kind is harmful to man, 
the change in its composition is sufficient to justify its 
condemnation as a food. 

When suppurating wounds or ulcerative or phleg- 
monous inflammations are present in any part of the 
body, there is danger of the milk being infected with the 
pyogenic organisms. 



INFLUENCE OF DISEASE UPON MILK 119 

EXCRETION OF MEDICINES THROUGH THE UDDER 
A number of medicines used in the treatment of dis- 
eased conditions in cattle are eliminated in part through 
the udder, namely: iodine, mercury, lead, copper, anti- 
mony, arsenic, salicylic acid, antipyrin, boric acid, aloes, 
rhubarb, senna, croton oil, euphorbium, morphine, strych- 
nine, atropine and veratrin. Although, under ordinary 
conditions, these substances are eliminated in the milk 
in small quantity, there is a possibility that milk from 
cows being treated with these drugs may be injurious to 
children and weak adults. When elimination through 
the normal channels is retarded by disease, they may be 
eliminated through the udder in larger quantity, and sub- 
stances which are not usually excreted through the udder 
may also pass out with the milk. For this reason milk 
should not be used for food from a cow which is being 
treated with medicines that are poisonous. Aloes, rhu- 
barb and senna affect the taste and color of milk. 

III. Diseases of Man Transmissible Through Milk 
Milk may act as a caiTier of the bacteria or virus of 
certain specific diseases of man. From time to time, 
epidemics in which the infectious agent has been dissemi- 
nated by milk have been reported, particularly outbreaks 
of typhoid fever, septic sore throat, diphtheria, and scarlet 
fever. These milk-borne epidemics have certain char- 
acteristics by which they may be recognized, viz: 1. The 
epidemic is explosive in character, a large number of cases 
occurring at about the same time, followed later by a 
rapid decrease in the number of new cases. 2. The dis- 
ease is limited to those families receiving their milk supply 
from a certain distributer; occurs in families using the 
greatest amount of milk and affects those individuals 



120 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

using the most milk, generally women and children. 3. 
The period of incubation is relatively short. 4. The dis- 
ease is of mild type. 5. The mortality is lower than usual. 
As a rule, the conclusion that the disease is dissemi- 
nated by milk must be based upon these characteristics 
and upon information obtained regarding the manner in 
which the milk may have been infected, rather than upon 
the demonstration of the infectious agent in the milk. 
The cause of scarlet fever is not known and consequently 
its presence cannot be detected by any known method of 
examining milk. The bacillus of typhoid fever has been 
demonstrated in milk several times, thus affording posi- 
tive proof that this organism is transmitted by milk, but 
the examination has been unsuccessful in a much larger 
number of cases. The diphtheria bacillus has been re- 
covered from milk in even fewer instances. There are 
several reasons why efforts to isolate these organisms 
from milk which is the cause of an epidemic may be unsuc- 
cessful. 1. Only a small quantity of the milk, a drop or 
two, is subjected to examination, and this may be free 
from the organisms even when the latter are relatively 
numerous in the whole volume of milk concerned. 2. The 
period during which the milk is infected may be termi- 
nated before it is suspected and examined. 3. The or- 
ganisms may be overgrown by the other kinds of bacteria 
which are present in milk in greater number. In prac- 
tice, the presence of these infectious agents in milk is 
not suspected until several cases of disease have appeared. 
Even if they could be detected in milk with more cer- 
tainty, it would be a mistake to defer action after an 
epidemic has started until the milk can be examined, 
because this would allow more time for the dissemination 
of the infection. 



INFLUENCE OF DISEASE UPON MILK 121 

TYPHOID FEVER 
Typhoid fever is more frequently spread by milk than 
any of the other infectious diseases of man except tuber- 
culosis. As a carrier of typhoid infection, milk is second 
only to water, although the cases caused by infected water 
greatly outnumber those resulting from infected milk. 
Milk may be infected with the Bacillus ty^phosus in sev- 
eral ways. The organisms may be introduced into milk 
when infected water is used to wash the milk vessels and 
utensils. Infected water may contaminate the milk when 
there is a leak in the milk cooler or when a can of milk 
is submerged in such water to cool. Water in open or 
thin-walled springs, surface wells, and in streams receiv- 
ing surface drainage may be readily infected by excre- 
tions from tj^phoid fever patients, convalescents, and 
chronic bacilli carriers. Milk bottles from houses where 
the disease exists may be a source of infection; one or 
two infected bottles may contaminate the water in which 
they are washed or rinsed, and this water will infect other 
bottles washed in it. A few bacilli introduced into a 
vessel or bottle by infected water will multiply rapidly 
when milk is placed in it, for the Bacillus typhosus grows 
abundantly in milk. Milk may be infected directly when 
the cows are milked or the milk or milk vessels are handled 
by persons affected with the disease, by convalescents, 
by chronic bacilli carriers, and by those attending typhoid 
fever patients. The greatest danger of direct infection 
is from those cases in which the disease is of such a mild 
type that it is not recognized, the so-called walking 
typhoid, and from chronic bacilli carriers, i.e., individuals 
who continue to excrete typhoid bacilli in the faeces and 
urine after they have recovered from the disease. It is 
estimated that 2 to 4 per cent, of typhoid fever patients 



122 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

become chronic bacilli carriers. The bacilli may also be 
carried by flies and be blown about in dust. 

The typhoid bacillus multiplies rapidly in milk and 
the number may be greatly increased in a short time. The 
milk is not changed in appearance. The organism grows 
in slightly sour milk ; it is checked or destroyed by a high 
degree of acidity, but it survives the degree of acidity 
existing in cream ripe for churning. It may live in milk 
several days and may be present in fresh butter and new 
cheese. Bruck found virulent bacilli in butter after 
twenty-seven days. Typhoid bacilli in milk are destroyed 
when exposed to a temperature of 60° C. (140° F.) for 
two minutes (Rosenau). 

When an outbreak of typhoid fever occurs which has 
the characteristics of a milk-borne epidemic, the sus- 
pected milk supply should be stopped, or pastem*ized 
under supervision, and an investigation made with the 
object of discovering and abolishing the source of the 
infection of the milk. Immediate medical attention to 
cases of illness affecting the dairyman, his employees, or 
members of their households, proper supervision of cases 
of typhoid fever by health authorities, the sterilization of 
milk bottles before refilling, and a pure water supply will 
greatly reduce the liability of the occmTcnce of such epi- 
demics. There is no method known which is entirely 
satisfactory in preventing the direct infection of milk by 
walking typhoid cases or by chronic bacilli carriers. 
Recently, some local health authorities have required that 
blood samples be taken from dairy employees and sub- 
mitted to the Widal test as a safeguard against chronic 
bacilli carriers ; a few high-class dairies have been follow- 
ing this plan for some time. Several states have laws 
requiring dairymen to report to the local health author- 



INFLUENCE OF DISEASE UPON MILK 123 

ities all cases of typhoid fever and other infectious dis- 
eases occurring in their own families and among their 
employees or in the families of the latter. 

PARATYPHOID FEVER 

Paratyphoid fever is also transmitted by milk, but 
less frequently than typhoid fever. The milk may be 
infected directly with the paratyphus bacilli by contact 
with persons affected with the disease or indirectly by 
polluted water being used to wash the milk vessels, uten- 
sils, and bottles. Water may be contaminated by fecal 
matter from infected persons. 

DIPHTHERIA 

A number of milk-borne epidemics of diphtheria are 
on record, although this disease has been less frequently 
disseminated by milk than typhoid fever. The diph- 
theria bacilli are present in the oral cavity and on the 
nasal mucous membrane of persons affected with the 
disease and may persist in these locations for months 
after the patient has apparently recovered. Persons 
who have attended diphtheria patients may also carry 
the bacilli. Infected persons may infect the milk directly 
or indirectly. In the beginning of some cases of diph- 
theria, the throat is apparently normal or only slightly 
aif ected. These cases and cases of chronic nasal diph- 
theria are most difficult to diagnose from clinical symp- 
toms. Because of the occurrence of cases of this type 
and the continuance of the bacilli in some individuals 
after the subsidence of clinical symptoms, it is not possible 
to guard entirely against the occasional infection of milk 
by the diphtheria bacillus. But the danger will be greatly 
reduced if prompt attention is given to all cases of sore 



124 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

throat occurring among dairy workers or in their fam- 
ilies; if persons who have attended diphtheria patients 
or individuals recovering from the disease are not per- 
mitted to handle milk or milk vessels until cultures from 
the throat prove to be free from the bacilli, and if re- 
turned bottles are sterilized before refilling. Frequently 
the bacilli are not very virulent. 

The diphtheria bacillus has been demonstrated in 
milk only a few times, principally because the organism 
is present in infected milk in small numbers and usually 
for only a short period. There is no doubt, however, of 
its transmission by milk. The milk is not changed in 
appearance by the growth of the organism. The bacillus 
is not affected by the degree of acidity present in cream 
ripe for churning, and it may therefore be present in 
butter and also in other dairy products, although we have 
no reports of the latter canying infection. A compara- 
tively low degree of heat is sufficient to destroy the 
organism. It is usually killed by a temperature of 55° C. 
(131° F.), but occasionally some individuals survive 
until the temperature reaches 60° C. (140° F.) . 

When an outbreak of diphtheria occurs with the 
characteristics of a milk-borne epidemic, the same pro- 
cedure should be followed as described under typhoid 
fever. 

SEPTIC SORE THROAT 

Epidemics of septic sore throat originating from in- 
fected milk have been reported from Eng-land for a 
number of years and, in recent years, several outbreaks 
of the disease, affecting thousands of persons, have oc- 
curred in this country. In some instances the infection 
of the milk was traced to cows affected with streptococcic 



INFLUENCE OF DISEASE UPON MILK 125 

mastitis, but in other cases there seemed to be reason to 
suspect that the milk had been infected by persons af- 
fected with septic sore throat (see page 111) . 

SCARLET FEVER 

Scarlet fever has been disseminated by milk more 
rarely than some of the other infectious diseases of man. 
The epidemics reported occurred principally in the 
United States and England. The infectious agent of 
this disease has not been discovered and it is not definitely 
known how it gains access to milk, but it is presumed 
that the milk is infected directly or indirectly by persons 
affected with the disease. The same action should be 
taken against a milk-borne epidemic of this disease as is 
indicated under typhoid fever. 

TUBERCULOSIS 

Tubercle bacilli of the human type have been demon- 
strated in milk (Hess, Rabinowitsch), and there would 
seem to be abundant opportunity for milk to be infected 
by a consumptive working in a dairy. Tuberculous 
individuals should therefore not be permitted to handle 
milk. 



CHAPTER VII 

DAIRY FARM INSPECTION 

The hygienic qualities of milk depend very largely 
upon the conditions existing at the source of supply. A 
knowledge of these conditions can be obtained only by an 
inspection of the dairy farm. Collecting a sample of milk 
in the city or town ^nd examining it in the laboratory 
will disclose certain conditions, and it will usually be cor- 
rect to infer that the same conditions exist in the entire 
volume of milk from which the sample was taken. Some 
of these conditions may be dangerous to the health of 
the milk consumer, but the milk will have been consumed 
before they have been discovered. Determining the 
number of bacteria per c.c. in a sample of milk will fur- 
nish a good basis for judging the care observed in pro- 
ducing and handling the milk, especially in regard to 
cleanliness and cooling, but it will not discover the pres- 
ence of the bacilli of typhoid fever, tuberculosis, or diph- 
theria, nor other important pathogenic organisms. Even 
if it were practicable to subject each sample of milk to 
the comprehensive examination necessary to discover 
these organisms, the milk from which the sample was 
taken would be consumed long before the examination 
could be completed. It is more rational to guard the 
milk against contamination at the source than to attempt 
to discover contaminated milk after it reaches the city 
and then exclude it from the supply. 

While it may not be possible to discover the actual 
contamination of the milk in all cases by inspecting the 
dairy farm, the conditions which permit or favor con- 
126 



DAIRY INSPECTION 127 

tamination can, with few exceptions, be discovered by a 
careful inspection. A proper laboratory examination of 
the milk in connection with the inspection will generally 
detect those conditions which may escape discovery at 
the inspection. The information obtained by inspection 
will serve as a basis for judging the quality of milk which 
may be produced, not only on the day of inspection but 
also thereafter. Moreover, inspection brings a repre- 
sentative of the health authorities into personal contact 
with the dairyman, a condition which should make for a 
better understanding and more sympathy on both sides. 
It is sometimes asserted that the bacterial testing of 
milk is more efficient in improving or controlling a milk 
supply than dairy inspection. This statement, however, 
will not bear critical examination. The ordinary bac- 
terial test merely approximates the number of clumps of 
bacteria present in a very small portion of milk. It does 
not determine the number of bacteria present, the kind, 
nor their source. It does not tell whether a high count 
is due to conditions existing at the dairy farm, during 
transportation, or at the distributing plant. It does not 
discover the presence of pathogenic organisms, excepting, 
perhaps, streptococci, and it does not indicate the source 
of these latter organisms. On the other hand, inspection 
of a dairy farm will disclose the physical condition of the 
cows, the sanitary condition of the premises, the char- 
acter of the equipment, the methods in use, and the physi- 
cal condition and proficiency of the dairyman and his 
employees. Dairy inspection alone will certainly furnish 
more useful information for judging the hygienic prop- 
erties of milk than bacterial testing alone. As an adjunct 
to dairy inspection, however, bacterial testing and other 
laboratory methods of examining milk are of great ser« 



128 IMMNCll'LMS AND IM{A(1'ri('K OK MILK IIVCIKNF, 

vice. I'lilcss hac'lcriul Icsling- is Lo he used only to find 
r.iulls ;iii(l no .'issisl.-mcc is lo Ik' od'crcd in correcting' 
llicni, it miisl l)c combined vviLli dairy inspection. 

Inspection of n diiiry riirm should include an exami- 
nation of (he roliowiiig: 

I. Slahle: 

I. hixterior. 
"2. Interior. 
11. Cows: 

1. Cleanliness. 

"2. Stai^-e of lactation. 

.'J. Symptoms of disease. 

III. Stahle practices: 

I. Cleaning- the slahlc. 
!lJ. Citaninj^- the cows. 
;{. MilUino;. 

l. I'eedino-. 
f). lU'ddini;'. 

IV. Milk House: 

I. lioeation. 

"2. Construction. 

.*{. A[)paralus. 

1-. Water sup|)ly. 

A certain sysix in oi* routine shoidd he followed in 
makinn" the inspeclion so that nolhinL>' will he overlooked. 
1 1 is usually con\ cnient lo heu^in with the stahle and then 
to follow the course of Ihe milk from here to the storat»;e 
cans or hollies, allhoui^h Ihe point of he^innini^' avIII have 
to he \ aric^l to suit the circumstances. The hest tinie to 
make an inspeclion is whiU> the cows are heini>' milked, 
hnt, unfortunately, all dairies caujjot he visited at this 
particular lime. The inspector sliould provide himself 



|)AII{,\ INSri'Ki'l'lON \'2\) 

will) n sull ol' lliiii, vv.isli.'iMc iiinJcri.'il lo piolcci liis 
cioiliin^-, and should niso wvnv Ji closc-lilliiio- c:\\) lo pro- 
tect liis liaii- while Hiiscullin^- Ihc Iiim.hs. IVIalcrijd of hlu(^ 
or a. darker eoloi" is luorc. desirahle Ihari while, because in 
stables where while; soils are nol, worn by Ihe milkeis 
some of tile cows are likely lo kick ai a, slran^(>r vvearin<^- 
white eloLhiii'Ji'. The inspeetion should be eai'ried out as 

follows: 

1. S'l'Am.M 

1. Exterior.- On approaching- the stable, the inspector 
should take note of: 

(a) The localiou. of the building- wilh regard to sur- 
face drainage. It is desirable lo have Ihe (loor of the 
stable about eight inehes above the suirounding ground 
and to have the adjoining ground slope away from llu; 
stable. 

{/;) 'I'lu; lypc of stable and its general eonstructtion 
— whether a bank barn with tlu; stable in the basement 
arid storage; space above for feed, or- a, one-stoiy stabU; 
entirely above the; ground; also, whether the building is 
constructed of stone, wood, or (;enu-nt. Information on 
these points may Ik; of value; late;r in the; ins|)e"e'tion in 
cenisidering the arrangements fe)r lighting anel ventila- 
tion. 

(c) KarjMhwre. — '^Fhe eliree;tie)n in whierh the winelows 
anel eloors fae-e' is e)f imporlaiie'e', as it has e-onsiderablc in- 
flue-ne'e; e)n the te;mperature; atiel lighting e)f the- intcrie)r. 
When the;re (;an be winelows anel eloors e)n e)nly one siele; 
of the stable; it is best to have; tlie-m fae-ing ihe se)iitli. 
This ex])e)sure' will permit the me)rning sun U* shine' into 
the stable and will keep enit the; he)t afiernoext sjin in 
sununer anel the' e-old winels in winter. When the- e*ows 
stand in a double row the ine^st desirable aiTangeme;nt 

9 



130 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

is to have the windows on the east and west sides with the 
two rows of cows extending north and south. The win- 
dows on the west side can be provided with wood shutters 
to keep out the sun on hot summer afternoons. When 
the shutters are up the flies will also be less troublesome 
on that side of the stable. 

(d) Surroundings, — The location of the manure 
dump and the direction of the surface drainage from 
the same should be observed, particularly with relation 
to the location of the source of the water supply. The 
accessibility of the manure pile to cows turned out for 
exercise or being driven into or out of the stable should 
also be considered. When cows are permitted to wander 
about in a lot of manure they become very much soiled, 
especially their legs and udders, and also carry a good 
deal of dirt into the stable. 

The proximity of other buildings, especially if used 
as horse stables, chicken houses, pigpens, etc., should be 
noted. Buildings used for these purposes, as well as 
manure piles, are breeding places for flies and are there- 
fore ob j ectionable when too close to a dairy stable or milk 
house. 

Attention should be given to the condition of the 
barnyard or exercise yard. Note its size and whether or 
not it is well drained. The condition of the barnyard 
has a considerable effect upon the cleanliness of the cows 
and stable. If it is muddy or dirty, some of this material 
will become attached to the cows and will be carried into 
the stable, increasing the labor of cleaning the cows and 
the stable. 

2. Interior of the Stable. — In examining the cow stable, 
the fact should be kept in mind that it is not only a shelter 
for animals but is also a place where human food is pro- 



DAIRY INSPECTION 131 

duced. Cows in milk should not be kept in the same 
stable with horses or other animals; they should have a 
separate stable for their exclusive use. There should be 
a special stable for parturition and for cows which are 
not in health. 

(a) Odor of the Air. — On entering the stable the 
odor of the air should be noted, since any slight abnor- 
mality will be more perceptible at this time than later, 
when the inspector has become accustomed to the atmos- 
phere. The odor of the air is a good test of the efficiency 
of the ventilation and also of the degree of cleanliness 
of the stable, especially in cold weather when the doors 
and windows are closed and the cows are kept in the 
stable almost continuously. Abnormal odors in stable 
air usually originate from two sources : exhalations from 
the cows and decomposing manure and urine. Condensa- 
tion of moisture on the walls, ceiling, or windows or the 
presence of frost is another indication of defective venti- 
lation. A moist atmosphere assists in the spread of tuber- 
culosis in a stable. The droplets of infected saliva ex- 
pelled by tuberculous cattle in the act of coughing float 
more readily in the stable air when it is satm-ated with 
moisture than when it is drier. In most instances cattle 
are infected with tuberculosis by the inhalation of in- 
fected air or by the ingestion of infected food or water. 
Insuflicient ventilation has the eif ect of concentrating any 
infection in the air of a stable, while ventilation dilutes it. 

Recent experiments have shown that the harmf ulness 
of insufficient ventilation is not due to a deficiency of 
oxygen, an excess of carbon dioxide, or the presence of 
organic poisons in expired air, but to the warmth and 
moisture of the air in unventilated places and to its lack 
of movement. A warm, moist atmosphere has a depress- 



132 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

ing effect upon the animal organism. It decreases the 
working capacity of the muscles and lowers the vaso- 
motor tone. It also causes a congestion of the nasal 
mucous membrane, rendering the animal more suscep- 
tible to respiratory infection. There is also reason to 
believe that metabolism is depressed. A moderately cool 
and moderately dry air in motion is the most healthful 
atmosphere for animal life. 

Ventilation. — The best system of ventilation for dairy stables 
is the one devised by the late Prof. F, H. King. Like other 
systems, it has inlets for the admission of fresh air and outlets 




Fig. 9. — Showing on the left how an inlet can be placed in a wall already constructed; 
on the right, how an inlet can be put in a wall being built; and in the centre, an outlet shaft 
with two openings — one just under the ceiling and one a foot above the floor. 

for the removal of impure air, but it has two features which are 
peculiar to it. The inlet flues are bent at a right angle, and 
the outside opening is lower than the inner one, the purpose 
being to prevent the escape of air from the stable through the 
inlets. The outlet flues are built from the floor up and have 
an opening near the floor as well as one near the ceiling, thus 
providing a means of drawing air not only from the upper 



DAIRY INSPECTION 133 

part of the stable, but also from the lower. Inlets are placed 
in all of the outer walls of the stable if possible, with the inside 
opening just under the ceiling and the outside opening five feet 
lower (Fig. 9). 

The number and size of inlets necessary will vary with 
weather conditions, and it is therefore desirable to have as 
many as possible and then use as many as may be needed. 
Weather conditions exert considerable influence on the air in 
stables ventilated by any system which depends for its opera- 
tion on natural forces. Wlien the atmosphere is still or moist, 
the ventilation is often inefficient in stables which under other 
conditions are well ventilated. 

A cow requires 59 cubic feet of air per minute and it is 
estimated that air will pass through a flue at the rate of 290 
to 300 feet per minute. The minimum number and size of 
inlets and of outlets required may therefore be calculated accord- 
ing to the following formula : ^ 

No. cows in stable x 59 ^ j^^ ^^ j^ ^ rp^^^j cross-sectional area in square inches 
300 of inlets and of outlets. 

By dividing the total cross-sectional area by the number of 
inlets and of outlets, the cross-sectional area of each inlet and 
outlet is ascertained. The number of inlets and of outlets will 
depend upon the size of the stable. Inlets should not be over 
12 feet apart; closer if possible. Several outlet flues of moder- 
ate size in different parts of the stable are preferable to one 
or two large outlets. 

Each inlet should be provided with a sliding door or other 
contrivance by which it can be conveniently opened or closed. 
The outlet flues should extend from the floor to 6 feet above 
the highest point of the roof and should be capped with a hood 
1 foot above the top. If they cannot be placed where they will 
not act as obstructions, they may be hinged at the ceiling so that 
they can be drawn up out of the way temporarily (Fig. 10). 
Each outlet flue should have two openings into the stable, one 
just under the ceiling and the other a foot above the floor, both 
openings being provided with doors which can be readily opened 

^ Wisconsin Exp. Sta., Bull. No. 266. 



134 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

or closed. The outlet flues must be air-tight and protected 
against cold in exposed places. The best material for the 
construction of these flues is galvanized iron (No. 28), 2x4 
inch lumber being used in the corners and joints. Where the 
shaft is exposed, the iron should be covered with %-inch boards. 
Outlets may also be constructed of a double layer of tongued 
and grooved boards with a layer of heavy building paper be- 
tween. If tin or galvanized iron pipes are used, they should 
be surrounded by a square wood frame and the interstices fiUed 




Fia. 10. — An outlet flue hinged at the ceiling bo that it can be drawn up out of the way. 

in with sawdust. Protection against cold is necessary because 
the air in the outlet flue must be kept warm, otherwise it will 
cease to ascend. The ceiling and walls of the stable should be 
air-tight and should be constructed with a view to preventing 
the radiation of heat as much as possible. 

The circulation of air through the stable results from the 
operation of two factors, called by Professor King aeromotive 
forces, namely: heat generated by the cattle, and wind. The 
wind drives air through the inlets on the windward side of the 
stable and thus increases the air pressure within the stable, as a 
result of which air is forced out of the stable through the outlets. 



DAIRY INSPECTION 135 

If the wind is very strong, air may also be forced out through 
the inlets on the leeward side, but ordinarily the right-angled 
bend in the inlets and the position of the outer opening at a 
lower level than the inner prevents or retards the escape of 
air through these inlets. In addition, wind passing over the 
top of an outlet shaft produces a suction action within the flue, 
and this draws air out of the stable. The force of this suction 
action increases with the height of the outlet shaft, because 
air movement or wind increases in velocity with the distance 
about the ground. 

The heat given off by the animals in the stable through 
the skin and in the respired air warms the stable air around them, 
expanding it and decreasing its density or weight, which causes 
it to rise toward the ceiling. Fresh air entering through the 
inlets, being colder and heavier than the air in the stable, gravi- 
tates toward the floor. Through the operation of these two 
currents the stable air and fresh air are mixed, the fresh air 
is warmed while the stable air is cooled and the moisture it 
contains is diluted. However, when the respired air is cooled 
below 81° F., it becomes heavier than fresh air of the same 
temperature because of the carbon dioxide which it contains and 
consequently settles toward the floor. For this reason, it is 
desirable to have the outlet flues arranged to draw air from 
the lower as well as the upper part of the stable. The expansion 
of the air in the stable by the animal heat increases the pressure 
within the stable and this has the effect of forcing air through 
the outlets ; the construction of the inlets prevents air from 
being forced out through them. To obtain satisfactory results, 
the air in the stable should be about 20° F. warmer than the air 
outside. The effect of temperature differences on the draft in 
outlet flues increases with the length of the flue. The resistance 
encountered by air in passing through inlets and outlets modifies 
to some extent the effects of wind and heat. It is therefore 
desirable to have the outlet flues as straight as possible. 

Cloth Method of Ventilation. — Stables may be ventilated by 
covering windows with muslin or cheese cloth. Glass windows 
should be alternated with the cloth-covered windows in order to 
permit sufficient light to enter the stable. Three square feet 



136 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

of glass and 2 square feet of cloth for each 1000 pounds of 
animal weight is a good proportion. When the air is still, a 
stable ventilated by means of muslin-covered windows will not be 
more than 1 to 3° F. colder than stables in which the King 
system is used, and there will be 7 to 10 per cent, less humidity 
in the stable air ; but when high winds prevail, the animal heat 
will be rapidly dissipated and the stable will be colder. If the 
cloth becomes wet and freezes, ventilation will cease. 

(b) Cubic 'Air Space. — This is determined by meas- 
uring- the length and width of the stable, multiplying the 
length by the width, and then multiplying the result thus 
obtained by the height of the ceiling. After the total 
cubic feet of air space has been ascertained in this manner, 
the stanchions or ties should be counted and the total 
cubic feet of air space divided by the number of 
stanchions. The result will be the cubic feet of air space 
per animal. The number of stanchions or ties should be 
used for this purpose instead of the number of animals 
present because this method will give the minimum cubic 
feet of air space per animal under all conditions. 

The size of a stable in proportion to the number of 
animals in it bears an important relation to ventilation. 
The less air space per animal the more frequently the 
air in the stable must be changed. The heat given off by 
animals is only sufficient to warm a certain quantity of 
air, and if this limit is exceeded the stable will be cold in 
winter. A stable with insufficient cubic air spaces will also 
be hot and uncomfortable in summer. 

It is desirable to have 1 cubic foot of air space for 
each pound of animal weight, but this amount cannot 
always be provided because of the cost of building mate- 
rials and for other reasons. With suitable arrangements 
for ventilation, 500 to 600 cubic feet of air space per cow 



DAIRY INSPECTION 137 

will answer quite well. A cow requires 59 cubic feet of 
air per minute, or 3540 cubic feet per hour. To provide 
this amount for a cow occupying a space of 500 to 600 
cubic feet, it would be necessary to entirely change the 
air in the space occupied by the cow six to seven times 
per hour. It is estimated that the heat given off by a 
cow in 24 hours is equal to 76,133 British thermal units, 
which is sufficient to heat 79,603 cubic feet of dry air 
from 0° to 50° F. This quantity of air would provide 
3316 cubic feet of air per hour, only 224 cubic feet less 
than the quantity required by the cow.^ It would appear, 
therefore, that the required amount of fresh air could 
be admitted to a stable with 500 to 600 cubic feet of air 
space per cow without lowering the temperature too 
much, especially since the temperature only rarely falls 
to 0° F. in the dairy sections in the northern part of the 
United States. The most comfortable temperature for 
the dairy cow is from 60° to 65° F., but if the temperature 
is kept lower by ventilation, say down to 50° F., the cow 
will not suffer in health and the milk flow will not be 
reduced, provided exposure to the low temperature be- 
gins in the autumn and is continuous. Milk cows have 
been kept through the winter in sheds open to the south 
with quite satisfactory results. 

The distribution of the cubic air space is important. 
If the ceiling is too high, the stable is likely to be cold at 
the level occupied by the cows, although the upper part 
may be warm enough. The height of the ceiling should 
be regulated by the size of the stable. Eight feet is a 
sufficient height for small stables. In a stable for 12 cows 

^ These figures are taken from Prof. F. H. King's book on 
" Ventilation." 



|;{S i'i(iN( 'ii'M'iM AND n{A(!'i'i(;ii; <»i'' mim-. iivcimni'; 

iJic <'<'ilifi/,' sliorild nol lie ovci- 10 IVcl lii;';li; Toi' «U) cows, 
not over 12 to If) feci ; riioic lli.'iii .*{() cows, not ovci- H» 
IVct (Hicvcl). 'VUc l(n..||. :in(l wi(llli(»r llie slal)l(! sIkmiM 
he Niicli iis will ()i()\ ulc NiiHicicnl lloor* spiifc to accoiii- 
riind.ilc I he cows (-oiiiroi'tMbly :iri(l lo iiinLc it (-onvciiKiil 
l(> iniik iiiul t'uic Inc llu'iii. Wlicii I lie cows slniid I'nciii;^' 
llic cciili'c of Ulc slnblc, Ihc ,'illc\' or |)ass.'(/j;(\\'.i\ iii \y.\vk 
of iJicm should \h' of siilliciciil \\ idlli to pcriiiil, llic |).iss.'i;j;c 
of n iii.'in c:ii-r'yiri/j^' a pail of milk willioiil llic |>.'iil loiicli- 
ill^" or coniiii;»; loo M<;ir llic cows. 'I'o iiiccl lliis rc(|iiii"c- 
Jiicril it \h neccNSai V lor iJie |)a,HNa,picway to be at least 
.'{ IVcl wide, tlic milk |>ail hciii/j;- carried on the sid(^ of the 
milk< I rarlhcsl Irom Ihc «-ow, hut a width of 5 or (> feet 
is much hcltcr. A narrow |)assa>»*eway back of Ihc cows 
iiiakcs il <liirKull to keep the wall clean. The passa«»'eway 
lu'twccn two rows of cows Ntandint!;- tail to lail sliould he 
at least H rc<l wide; it can hardly he wide enough to 
])revenl milk carried in a pail hetween the cows from he- 
illg" coiilamiiialcd hy Ihc dust dislod;j;<'d liy tlus\\ itching" 
of tlie tails. There is also danjLJ;"cr of contamination from 
S|)lasliin;j;' urine and manure. 

'I\> [>ro\ idc r)(M> lo (■>()() ciihu' feet of air space [)er cow 
Ihc Ihtor space, with a 1) foot cciliii;.'-, may l)e distrihuted 
as follows: 

l'\c<l iilk'V 'I* fi'^'l' 

Miui^v.- IVij to 2 foot 

iMMllorm tl/. loSy- foot 

(Jill 111- 10 iiiehos 

iMIi'V III real" <>l ••own t> lo ("» li'ft 

The total of these dimensions would he 18 feel. Al- 
lowinpf 8V2 feet lor the witllh of the stall, there would he 
(>.*{ S(|uarc feel of lloor space lor each ccmv, w hicli, w ilh a 



DAIKV INMI'I'ldlON 189 

ceilin/^' i) (ccl lii^li, would (jiovidc r><>7 <ul)ic IVrl of ;i,ir 
spucc j)ii- cow. Willi llic <'ows sbiiidiii^- in I wo rows, l,li»^ 
stjihlc would he «{(> IVcl, wide, wliicli is iiol loo wide for il, 
lo In- vvrll li^lilcd il' witidows :ir<' plnccd on lioUi sides. 
It will llii re lojc l)c seen llial, lln- necessary are;i of llocjr 
space to make llie <'ows coinlorlaM*' ;iiid l,li(t sl;d»lc woik 
coiivenieiil, will also provide a lair ainoiiiil, of ciihic air 
si)ace. 

{c) Interior Cfmnirncllon. 'I'lie inalcrial used in 
the construction of lJuM'(M I itipi", walls. Moor, plaU'orm, r«cd 
trough, droj) oi- /^iiller, ain! slall lillinp^s, iJieir slalc <»!' 
rc^paiiarid llieir eon<lilioii in r(7.';ar<l l,o cleaidiness should 
he nolt;d. While delecls and dedcieneics in slsdile ("on- 
struelion may he overcome to a, eorisiderahU^ extent hy 
careful and painstakin/j;' methods, al, iJie sa,m<' liine a, 
properly constructed and convenienlly arran/^ed stahle 
saves lahorand therefore eneoura/^es I.Ik' |)i"a('l,i(;(; of ^ood 
methods; it also adds to llie eoml'ort of the cows and con- 
sequently increases their productiveness. 

'IMic (uiliiK/ should he li^^hl, and smooth, plastered, 
painted, oiled, oi' whit(;wa,shed, and [vva- froiri col)w<ths. 
There is no oh jection to storing hay or fodder ahov(' the 
cow stahle if the ceiling' is ti^ht. It is Ixttei- not to have 
any ojxrjin/^s in \\\v. ceiling- throu/^li whicli hay, fodder 
or straw may he thrown down into thct stahle; hut if 
there must he such openin/^s, Ihey shoidd he in front of 
the (!ows and not in tlie rear. 

Tlie tvallH shoidd he smooth and cl( an. 1 1 is desira[)lc 
to have the inrjer surfaxMt of the walls hack of Ihc cows 
finished smooth with cement for at least 4 f(Mtt a,l)ov<' th<; 
floor and covered with an impervious paird, from wliich 
dirt can he readily removed hy washing. Where paint or 
cement (tan not he used, the application of whitewash will 



140 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

improve the conditions. Any woodwork can be treated 
in the same manner. Whitewashing removes dirt and 
cobwebs, improves the light, and exerts a disinfectant 
action. 

The platform, or the floor of the stall, should be about 
8 inches above the bottom of the drop or gutter and 
should be smooth, free from cracks or depressions and 
impervious. All things considered, cement is probably 
the best material cf which to construct platforms. 
Cement platforms are objected to on the ground that 
they are slippery, cold, and hard. If given a rough 
finish with a wood trowel or by drawing a stiff broom 
over the surface before the cement is dry, they will not be 
slippery. A layer of coal tar or pitch about 1% inches 
below the surface will reduce the conduction of heat from 
the body of the cow and will therefore make the platform 
warmer, while the hardness can be overcome to a certain 
extent by the use of plenty of bedding. Recently, a 
mixture of two parts of sawdust and one part of cement 
has been recommended in place of the usual cement mix- 
ture, the claim being made that it is warmer and is not as 
slippery. A covering of inch boards is sometimes laid 
down over the cement to reduce the hardness and cold- 
ness. Cement floors have several advantages; they are 
readily cleaned, wear well, and do not absorb urine or 
liquid manure nor permit these substances to leak through 
and saturate the earth beneath. Next to cement, the 
most desirable floor is one of matched planks, with the 
joints filled with tar. Wood is less of a heat conductor 
than cement and is not as hard, but it absorbs urine and 
liquid manure and is liable to crack and form crevices in 
which manure and other material may lodge and decom- 
pose; it is also less durable than cement. Cork bricks 



DAIRY INSPECTION 141 

laid on concrete are also used for platforms and floors. 
It is claimed for them that they combine the good prop- 
erties of cement and wood and at the same time do not 
have any of the undesirable properties of those sub- 
stances. An earth floor is most objectionable. Unless 
plenty of good absorbent litter is used it is very likely 
to be wet and dirty; it finally becomes saturated with 
urine and liquid manure, which decompose and liberate 
foul-smelling gases. 

The rear 18 inches of the platform should slope 
sHghtly toward the gutter, just sufficient to cause liquids 
to flow in that direction. Too much slope is likely to 
cause the cow to slip ; it also causes the cow to stand down 
in the gutter and favors prolapse of the vagina and 
similar troubles. It is desirable to have a depression in 
the front of the platform % inch deep and extending 
back about 18 inches from the anterior border. This will 
prevent cows from falling on their knees when attempt- 
ing to rise or when reaching for feed, and will also have 
a tendency to keep the litter from being pushed toward 
the rear of the stall (Fig. 11). 

The length of the platform is important ; if too long, 
the faeces are dropped where the cow can lie upon them ; 
if too short, the cow is uncomfortable and stands down 
in the gutter. The proper length is 4% to 5% feet, 
differing with the size of the cow. Frequently, where 
a number of cows stand in a row, the platforms are made 
41/2 feet long at one end with a gradual increase to 5I/2 
feet at the other end of the row, thus supplying platforms 
of different lengths on which the cows can be placed ac- 
cording to size. The platform for each cow should be 
31/2 to 4 feet wide, depending upon the size of the cow. 
The width is quite as important as the length, because 



DAIRY INSPECTION 143 

if the stall is too wide and the cow stands diagonally 
the result will be the same as if the platform was too 
long. The stall should be constructed with the view of 
preventing the dropping of manure where the cow can 
lie down upon it, in so far as this is possible, and thus 
save labor in keeping the cow clean. Other points to 
be considered are the comfort of the cow, convenience of 
cleaning the stall, milking, and feeding, and the cost. 

The feed trough or manger may be built of wood or 
cement. Cement is better because it is easier to keep 
clean. A continuous cement trough, extending in front 
of a row of cows without any divisions, can also be used 
for water. In addition, the continuous trough is more 
conveniently cleaned, but on the other hand it favors the 
spread of infectious diseases, especially tuberculosis. 
Feed placed before a tuberculous cow may be contami- 
nated by infected saliva and material ejected in cough- 
ing, after which it can be readily obtained by cows in 
adjoining stalls; the tuberculous cow may also contami- 
nate the feed of the cows standing on either side, and also 
of cows standing opposite, and when water is run into 
the trough infection may be carried from one end of it 
to the other. On the other hand, separate feed troughs 
or mangers, although decreasing the danger of infec- 
tion, increase the labor of cleaning; they also make it 
necessary to have individual drinking cups or to drive 
the cows to water outside of the stable. When a herd is 
regularly tested with tuberculin and the reactors 
promptly removed, and when the trough is swept and 
washed daily, the danger of infection from the common 
feeding trough is greatly reduced. The bottom of the 
feed trough should be 2 inches higher than the level of 
the platform. When cows have to reach too far for their 



144 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

feed, the front feet frequently slip backward and the 
cows are thrown on their knees, causing bruises which 
often lead to the development of knee tumors. The feed 
trough should be 18 inches wide and at least 6 inches 
deep, with the front high enough to prevent feed from 
being pushed out of it. 

The gutter or drop should be constructed of cement. 
Wood or earth gutters cannot be kept clean and free 
from odor. The gutter should be 16 to 18 inches wide, 
with an average depth of 8 inches below the level of the 
platform. It should be deeper at one end than at the 
other, to give the bottom sufficient slope for drainage, 
or the entire floor may be sloped and the depth of the 
gutter remain the same. Sometimes the floor back of 
the platforms is laid on a level with the bottom of the 
gutter or 2 or 3 inches above it, thus removing the back 
wall of the gutter entirely or making it 4 or 5 inches lower 
than the front wall. This has the advantage of per- 
mitting the sun to shine into the gutter when there are 
windows in the rear of the cows, but it also increases 
the likelihood of manure being splashed upon the wall; 
when the back wall of the gutter is lacking entirely there 
is a tendency for the hind feet of cows to slip backward 
when they are stepping up onto the platform. Plenty 
of litter should be kept in the gutter to absorb the urine 
and thus prevent it from being splashed by droppings 
or by the cow's tail when the animal is lying down and 
switching at flies. The floor of the gutter sometimes has 
a % inch slope from the front to the rear with the object 
of raising the toe and increasing the tension upon the 
posterior tendons when cows stand down in the gutter, 
the intention being to make the position uncomfortable, 
but this construction does not always have the desired 
effect. 



DAIRY INSPECTION 145 

Ties or Stanchions. — From a sanitary standpoint, 
stanchions or jacks are better than chains because they 
are more likely to hold the cow in the proper place in the 
stall to cause the manure to be dropped into the gutter, 
thus assisting indirectly in keeping the cows clean. The 
swinging chain-stanchion is also quite comfortable. The 
best material for stanchions and their supports is metal 
piping. 

Stall divisions help to keep the cow in place and thus 
assist in keeping the platform and the cow clean; they 
also prevent the cow from treading on the udder or teats 
of a neighboring cow. Solid, board partitions, extending 
from the floor upward, are objectionable because they 
increase the difficulty of keeping the stable clean and 
interfere with the circulation of air ; they may also be in 
the way of the milker. Wood fittings with flat surfaces 
and cracks are not as easily kept clean as round, smooth 
surfaces, and the cracks make disinfection more difficult. 
Stall divisions consisting of a single piece of metal pipe, 
extending in a curve from the front post of the stall to 
the rear of the platform, with a radius of 3 feet, are not 
open to these objections. 

Arrangement of the Stalls. — ^When stalls in a stable 
are placed in two rows, they are arranged with the cows 
in one row facing those in the other, with the feed alley 
in the centre between the mangers, and a passageway in 
the rear between the manure gutter and the side wall ; or, 
the stalls are arranged with the cows in each row facing 
outward toward the side walls, with a feed alley in front 
of each row between the manger and the wall and a pass- 
ageway extending through the middle of the stable be- 
tween the two rows of cows. Both plans have advan- 
tages and disadvantages. When the cows stand facing a 

10 



146 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

central feed alley, feeding is facilitated and, if there are 
windows in the side walls, the posterior part of the cow 
is in the lightest part of the stable, which is a convenience 
in cleaning the cow and in milking; but the spread of 
infection is favored because material coughed out by one 
cow may be deposited in the feed trough of the cow 
standing opposite in the other row. With the cows fac- 
ing outward toward the side walls, the cleansing of the 
stable and the removal of the manure is facilitated and 
there is less exposm-e to infection by coughing, but the 
cleaning of the cow and the milking must be done in 
the darkest part of the stable and the milk must also be 
carried between the two rows of cows and is thus exposed 
to external contamination, especially in the fly season 
when the cows frequently switch their tails. 

Matertiity and hospital stalls should be provided in 
another part of the building or in another building. If 
there are not special stalls for these purposes, cows with 
vaginal discharge from retained placenta and with other 
pathological excretions will be stabled in the milking line 
and may infect the milk indirectly. 

{d) Light. — The cow stable should receive sufficient 
daylight to make it possible to read ordinaiy newspaper 
print in the middle of it. This much light is necessary for 
the cleaning and the milking of the cows to receive proper 
attention. Nearly all of the work which must be done in 
a cow stable can be done better and easier in the light than 
in the dark. The admission of sunlight into a stable is 
beneficial in several respects. It lights the stable and 
exposes dirt, thus assisting in keeping the stable and 
cows clean; it facilitates careful milking; assists in dry- 
ing out the stable ; supplies some warmth to the stable in 
winter, and has a disinfectant action. The germicidal 



DAIRY INSPECTION 



147 



effect of sunlight is not fully appreciated. Experiments 
with artificial cultures of various bacteria have shown 
that direct sunlight is very destructive to germ life, while 
the action of diffused light, although less powerful, is also 
quite effective. Tubercle bacilli are killed by direct sun- 
light in a few hours, while even diffused daylight destroys 
them in a few days (Koch). 
Direct sunlight kills anthrax 
spores in five hours and the 
bacilli in thirty hours, spores 
being more susceptible to 
sunlight than bacilli (Ar- 
loing, Roux). Direct sun- 
light destroys or decreases 
the virulence of colon bacilli, 
the bacilli of fowl cholera 
and swine erysipelas, and the 
virus of hog cholera, while 
diffuse daylight also exerts 
a similar but less powerful 
action (Neumark). 

The inspector should 
note the location and size of 
the windows and determine 
the total square feet of win- 
dow surface. He should 
also observe whether the 
glass is clean and if other buildings obstruct the en- 
trance of light. Three to four square feet of win- 
dow surface for each cow will usually admit sufficient 
light, provided the windows are properly placed and 
equally distributed. In cold climates, an excess of win- 
dow surface may increase the radiation of heat to such an 




Fig. 12. — Window arranged to act as a fresh 
air inlet (Wis. Exp. Sta. Bull. No. 266). 



148 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

extent as to interfere with ventilation; this can be avoided 
by constructing double windows, with an air space be- 
tween. Where cows stand in a double row, a row of 
windows along each side of the barn is very desirable. 
The windows may be hinged at the bottom and arranged 
to open and close by turning a continuous rod; or they 
may be unattached, as many prefer, and merely rest in 
a groove in the window sill, being held in place by a peg 
near the top. If the vandows are to be used as inlets for 
ventilation, the openings formed at either side when the 
sash is inclined inward at the top should be closed by 
boards or galvanized iron strips extending inward from 
the window frame on each side. The galvanized iron 
shields prevent the wind from entering at the sides and 
blowing directly upon the cattle (see Fig. 12). 

The arrangements for artificial lighting should be 
noted. These are rather important, for much of the work 
in the stable in winter is done before and after daylight. 

II. cows 

The examination of the cow is one of the most impor- 
tant parts of dairy inspection. If the cows are not in the 
stable at the time of the inspector's visit and if it is not 
convenient to bring them in, this part of the inspection 
should be made at a more opportune time, but the inspec- 
tion of the dairy should not be regarded as completed 
until the cows are examined. No attempt should be made 
to examine the cows while they are running free in the 
pasture or exercise lot, unless each one can be readily 
caught and handled. 

1, Examination for Cleanliness. — Observe the condition 
of the cows with regard to cleanliness, especially the con- 



DAIRY INSPECTION 149 

dition of the flanks and udder. The condition of the 
cows in tliis respect is usually an indication of the care 
they receive and of the efforts made to keep the milk 
clean. It is not necessary for the inspector to be present 
when the work is done in order to determine if the cows 
are regularly cleaned. When cows are regularly 
groomed, the posterior quarters are comparatively free 
from dried manure and the hair coat is smooth and some- 
what glossy. The hair is also shorter and thinner than 
on cows which are not regularly brushed. Clipping the 
hair short on the udder, flanks, buttocks, and tail, and 
cutting three or four inches off the switch if it touches the 
floor, is of great assistance in keeping the cows clean, and 
evidence of clipping is an indication that the cows are 
regularly groomed. Exfoliations from the skin and par- 
ticles of dirt are likely to collect in the hollows about the 
root of the tail and their presence in any great quantity 
points to carelessness or neglect in cleaning. Fresh 
manure on the buttocks (point of ischium) is not neces- 
sarily an indication that the cow was not properly cleaned. 
These parts are readily soiled if, during defecation, the 
tail is pressed down on the faeces and is subsequently 
moved from side to side. 

2. Stage of Lactation. — Examination and inquiry 
should be made regarding the stage of lactation. The 
daily milk record, if available, will be of gi*eat assistance 
in discovering cows near the end of lactation. When the 
milk flow has decreased to a quart ( 2 pounds ) a day or 
less, the milk is likely to have a salty taste or a strong, 
cow-like odor and taste, and in many cases the cream will 
not " butter." Such cows should be " dried off." The 
secretion of fresh cows should be examined for the char- 
acteristics of colostrum. 



150 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

3. Examination for Symptoms of Disease. — This exami- 
nation consists of two parts: (a) General examination 
and (b) special examination. 

{a) GENERAL EXAMINATION 

The general examination is made first, with the cow 
in the stall. Taking a position in the rear and slightly 
to one side, the inspector proceeds with the examination 
in the following order: 

1. Attitude. — Note the general appearance, the car- 
riage of the head, position of the ears (erect or hanging) , 
standing position, behavior ( quiet or restless ) . 

Dullness or depression from fever, also weakness and pain 
may be discovered in this way. Very sick animals and those 
with a high fever usually hold the head low, with the ears 
drooping. In severe vaginitis and metritis, and sometimes in 
constipation and colic, cows stand with the back arched, head 
lowered, tail elevated, and legs spread apart. Sometimes cows 
affected with vaginitis stand a long time in the attitude of 
urination. An arched back and erect hair, in association with 
shivering and a cold skin are symptoms of fever, although they 
are not constant. In dyspnoea and sore throat the head is 
extended. Pain causes restlessness ; soreness of the extremities 
is indicated by resting the affected hmb, or, when more than one 
limb is affected, by continually shifting the body weight from 
one leg to another. Cows often lie down during the day, espe- 
cially after eating, and do not rise on the approach of man; 
therefore, a recumbent position is of less significance with these 
animals than in the case of the horse. A disposition to lie down 
continually may be due to articular rheumatism or to osteo- 
malacia. Inability to rise is caused by paralysis (spinal frac- 
tures), milk fever, and ante and postpartum paralysis. Some- 
times refusal to rise is due to stubbornness. 

2. Skin and Hair, — Observe the condition of the skin 
and hair and look for swellings, enlargements and irregu- 
larities of form. 



DAIRY INSPECTION 151 

Rough, bristling, lustreless hair and a dry, stiff skin (hide- 
bound) indicates unthriftincss or lack of condition, which may 
be due to disease or improper care. In stables in which the 
cows are regularly groomed, fresh cows, especially heifers with 
the first calf, may appear rough and thin in comparison with the 
other cows for a week or two after they are placed in the milk 
stable. This condition is due to the effects of parturition and 
to not being regularly groomed previously ; it must not be con- 
fused with unthriftiness. When associated with a good appe- 
tite, unthriftiness and progressive emaciation are indications 
of chronic disease, frequently of tuberculosis. Emaciation, 
however, may be due to old age. Mere thinness must not be 
mistaken for unthriftiness or emaciation; heavy milking cows 
are often thin. The condition of the skin and hair is a better 
indication of the actual physical condition than the degree of 
fleshiness or leanness. 

Swellings may occur in or beneath the skin (local inflamma- 
tions, oedemas, abscesses, enlarged lymph glands, actinomycosis, 
etc.) and suppurating wounds may involve the skin and sub- 
cutaneous structures. Distension of the left side of the abdomen 
occurs in impaction and tympanites of the rumen. 

3. Vulva, AntLS, and Tail. — These should be ex- 
amined for evidences of pathological discharges. Dis- 
eases of the uterus, vagina, and digestive tract may be 
discovered in this way. There are certain normal dis- 
charges from the vulva which must not be mistaken for 
pathological discharges. A small amount of glassy 
mucous, frequently blood-stained, is discharged during 
oestrum; a bloody or grayish albuminous discharge is 
sometimes seen after breeding, while near the end of 
pregnancy there is usually observed a glassy mucous dis- 
charge which is often of a red color. 

A foul, chocolate-colored or reddish fluid containing frag- 
ments of tissue is discharged from the vulva following retention 
of the placenta. In metritis and vaginitis the discharge is either 



152 TRINCIPLES AND PRACTICE OF MILK HYGIENE 

colorless or yellow, red or chocolate color, thin at first and 
gradually becoming thicker. In chronic metritis the discharge 
is white, sticky, and odorless, or muco-purulent, purulent, or 
chocolate-colored and foul-smelling. A slight purulent dis- 
charge occurs in tuberculosis of the uterus. When the discharge 
is slight it may be observed only when the cow lies down or its 
presence may be indicated only by a soiled condition of the tail. 
The vulva is swollen in metritis and in puerperal septicjemia. 
In tuberculosis of the uterus the vulva is flabby and the broad 
ligaments are relaxed and sunken. Relaxation of the broad 
ligaments also occurs m ovarian disease and frequently in 
aged cows. 

If defecation does not occur during the examination the 
character of the bowel discharges may be determined by ex- 
amining the manure in the gutter or drop and by observing the 
condition of the tail and buttocks. Soft bowel discharges, if 
general, may indicate a sudden change in feed, overfeeding, or 
the feeding of spoiled feed, as well as disease. Dry, hard faeces, 
often of a darker color than normal, are seen in constipation 
and in severe febrile disease ; soft or semi-fluid faeces in intestinal 
catarrh, advanced tuberculosis of the mesenteric lymph glands, 
pseudo-tuberculosis or Johne's disease and enteritis ; red, choco- 
late-colored or black fseces in hemorrhagic enteritis and dysen- 
tery. Blood is present in streaks or clots in hemorrhage of the 
rectum and bloody discharges occur in anthrax. Coarse par- 
ticles of food in the fasces indicate disturbance of rumination in 
consequence of impaction, torpidity, or paralysis of the rumen. 

4. Respiration. — The rate, rhythm, intensity, and 
character of the respiratory movements can be deter- 
mined by observing the movement of the flanks. 

Rapid breathing is often seen in advanced pulmonary tuber- 
culosis, but it is not a constant symptom. The rate of respira- 
tion is increased in other diseases of the respiratory tract, in 
fever and in painful conditions. An increase in the respiratory 
rate occurs also immediately after eating, after exercise, and in 
hot weather. Increase in the intensity or depth of the respira- 



DAIRY INSPECTION 153 

tory movements is a symptom of disease, except when it occurs 
after exercise. A decrease in the intensity or depth (shallow 
respiration) is observed in pleurisy and in painful conditions 
of the chest wall. 

5. Udder. — Examine the udder by inspection. This 
can be done best when the udder is full. Compare the 
form and size of the different quarters. Look for swell- 
ing (mastitis), atrophy, furuncles (feed boils), altera- 
tions of cowpox, etc. 

6. Appetite. — Look into the manger and see if the 
feed has been eaten and note if the animal is ruminating. 

7. Muzzle and Nostrils. — Touch the muzzle and 
determine the degree of temperature and moisture. Ex- 
amine the nostrils for pathological discharges. 

The muzzle is dry and sometimes roughened in fever and 
diarrhoea. It is alternately hot and cold in fever, and cold and 
dry in low conditions endangering life. Vesicles occur on the 
muzzle in foot and mouth disease. 

A discharge from the nostrils occurs in exudative diseases of 
the respiratory tract, but in tuberculosis the discharge is 
frequently not present because the exudate is usually coughed 
up and swallowed. A nasal discharge may escape notice in 
cattle because it is generally licked off with the tongue. It is 
most likely to be seen after coughing. A slight mucous dis- 
charge is normal. 

8. Suhmojoillary and Peripharyngeal Regions. — At- 
tempt to palpate the submaxillary, parotid, retropharyn- 
geal and atlantal lymph glands ; they cannot be felt unless 
enlarged. 

The submaxillary lymph-gland is situated within the pos- 
terior angle of the lower jaw, between the sternocephalicus 
(sternomaxillaris) muscle and the submaxillary salivary gland. 



154 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

The subparotid lymph-gland is about 2^/2 inches long, flat 
and tongue-like in form and is located just under the anterior 
border of the parotid salivary gland and about 3 inches below 
the base of the ear. In feeling for this gland press the finger 
inward and backward in the groove between the posterior border 
of the lower jaw and the parotid salivary gland. 

The retropharyngeal lymph-gland, also called the pharyn- 
geal and superior pharyngeal, is about 2 inches long and is 
situated on the posterior wall of the pharynx. It can be pal- 
pated, when enlarged, by pressing the extended fingers inward 
from each side toward the median line and as far forward as 
possible between the muscles of the neck and the larynx. 

The atlantal or posterior retropharyngeal lymph-gland is 
situated under the wing of the atlas, partly covered by the 
upper end of the submaxillary salivary gland. By pressing the 
fingers inward and upward under the wing of the atlas this 
gland is forced against the under surface of the wing of the 
atlas. 

When any of these glands in cattle are enlarged and firm 
and not hot or painful, tuberculosis is usually present. En- 
largement of the retropharyngeal glands may interfere with 
swallowing and respiration. 

Actinomycotic tumors may be observed in the submaxillary 
and peripharyngeal regions as well as in the maxillse and tongue. 

0. Cough. — Test each cow for cough by exerting 
pressure with the fingers on the larynx or first three 
rings of the trachea, or close both nostrils for about a 
minute; also grasp the skin over the withers with the 
fingers of both hands and draw it upward. Take note 
of any coughing which occurs spontaneously and identify 
the cow each time. 

A frequent, chronic cough is one of the most prominent 
symptoms of pulmonary tuberculosis. If a cow can be made 
to cough by pinching the larynx or the adjoining rings of the 
trachea, or by closing the nostrils, it is an indication of disease 
of the respiratory tract. Cough can usually be induced in this 



DAIRY INSPECTION 155 

way in advanced tuberculosis of the lungs ; if the cough is low, 
weak, and moist, it is especially suspicious. Old cows are not 
infrequently affected with pulmonary emphysema, and a short, 
dry cough may be readily induced in such animals ; but even a 
cough of this character is suspicious of tuberculosis. A cow in 
health may cough as a result of inhaling dust, cold air, or irri- 
tating gases, but the cough is not frequent or chronic. Cough 
in cattle is softer, hollow (toneless), and more prolonged than 
in the horse. 

If drawing the skin up over the withers produces cough, it 
is an indication of an irritated condition of the lungs or pleura. 

10. Lungs. — The lungs should be examined by aus- 
cultation. In doubtful cases, closing the nostrils for a 
short time or exercise will render the sounds more 
audible. 

Exaggeration of the vesicular murmur (when not due to 
exercise) and the presence of the bronchial sound, rales, or 
vague sounds are evidences of disease of the bronchi or lungs. 
Friction sounds occur in pleuritis (fibrinous). In tuberculosis, 
especially after exercise, the vesicular murmur may be exagger- 
ated and rough, and rales and vague sounds may be heard. The 
disease may exist, however, when no abnormal sounds can be 
detected. In old cows sibilant rales may be heard because of the 
presence of pulmonary emphysema. 

11. Prescapular and Precrural Lymph-glands. — ■ 
The precrural glands can be palpated whether normal 
or enlarged, but the prescapular glands cannot be felt 
unless they are enlarged. 

The prescapular lymph-gland, also called the superficial 
cervical, is situated beneath a layer of muscular tissue at the 
anterior border of the shoulder, a little above the shoulder 
joint. 

The precrural lymph-gland is situated in the flank, just 
under the skin, at the anterior border of the tensor fascias 



156 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

lata muscle. Normally, it is about 1 inch in width and 4 to 6 
inches long. 

When these glands are enlarged, firm and not hot or painful, 
they are usually tuberculous. The lymph-glands are also en- 
larged in leukaemia and pseudoleiikjemia, but in these diseases all 
of the superficial lymph-glands on both sides of the body are 
similarly affected. 

12. Complete the E anamination of the Udder and 
Examine the Supramammary Lymph-glands. — Inspect 
the skin of the udder and teats for furuncles, ulcers, 
symptoms of cowpox, etc. Inspect the opening of the 
teat canal for scabs. 

Palpate the udder. This is done most satisfactorily 
when the udder is empty. Beginning with the inferior 
extremity of the teat and passing upward, palpate suc- 
cessively the teat canal, the milk cistern, the gland tissue 
and the supramammary lymph-glands. Note the tem- 
perature of the parts and look for symptoms of acute 
inflammation, indui-ation, and nodules. By rolling the 
teat between the fingers, thickening of the mucous mem- 
brane of the cistern and nodular formations in the walls 
of the cistern and teat canal can be detected. In palpat- 
ing the udder, pass one hand up between the two halves 
of the organ, place the other hand on the external surface 
and then, beginning at the posterior or anterior extremity, 
slowly work the udder tissue between the fingers, search- 
ing for indurations, retention cysts, etc. 

Draw milk from each quarter into the palm of the 
hand and examine it for color, consistency, flakes, clots, 
etc. In doubtful cases collect a sample for further 
examination. Press the end of the teat to see if any 
mucus or pus can be squeezed out of the teat canal. Ob- 
serve if there is any difficulty in expressing the milk from 



DAIRY INSPECTION 157 

the teat and if the stream is split or deflected from the 
normal direction. 

Palpate the supramammary lymph-glands. Stand- 
ing in the rear of the cow, press the hand forward along 
the upper and posterior margin of the udder, with the 
thumb on one side of the median line and the fingers on 
the other, and grasp the glands by bringing the fingers 
and thumb together. Ordinarily, these glands are about 
2 inches in diameter, but in heavy milkers they may be 
larger. 

Pronounced swelling, excessive heat, and pain in one or more 
quarters of the udder, with marked changes in the milk, are 
symptoms of parenchymatous mastitis. 

Firm nodules which are neither hot nor painful, or a rather 
diffuse induration which is painless and without heat, in one or 
both posterior quarters, with enlargement of the supramam- 
mary lymph-glands, are symptoms of tuberculosis of the udder. 
There is no apparent alteration of the milk during the first 
stages of the disease. Indurated areas of greater or less extent 
result also from parenchymatous and catarrhal mastitis, but 
they are not accompanied by enlargement of the lymph-glands, 
except in the acute stage. 

Enlargement of the supramammary lymph-glands is asso- 
ciated with tuberculosis of the udder and also occurs during 
acute mastitis. These glands may be enlarged as a result of 
tuberculous infection when no symptoms of the disease are 
apparent in the udder. 

Difficulty in expressing milk from the teat and deflection 
or division of the milk stream are early symptoms of catarrhal 
mastitis. If pus or mucus can be squeezed out of the teat 
canal, catarrhal mastitis is present. A scab may be found over 
the opening of the teat canal when this disease exists, although 
clots or flakes of dried milk are sometimes present when the 
udder is normal except for some defect in the sphincter ap- 
paratus of the teat. The milk may appear unaltered or show 
only slight changes when these symptoms are present. 



158 PKINCIPLES AND PRACTICE OF MILK HYGIENE 

A thick cord-like induration, about the thickness of a lead 
pencil, extending vertically through the middle of the teat, is a 
symptom of catarrhal mastitis ; also nodular indurations in the 
walls of the teat canal and milk cistern. Only slight alterations 
may be present in the milk, or none at all. 

Atrophy is usually a symptom of an existing or previously 
existing catarrhal mastitis. Milk from the affected quarter 
may contain the organism responsible for the condition even 
when it shows no perceptible changes. 

(For the changes in milk occurring during udder disease 
see pages 105-110.) 

Firm, nodular swellings, not hot or painful, situated in the 
superficial parts of the udder tissue, which are not movable and 
which can be reduced by strong pressure, are retention cysts, 
formed by the blocking of the milk ducts. 

(6) SPECIAL EXAMINATION 

The character of the special examination will depend 
upon the information obtained during the general 
examination. 

If fever is suspected the temperature should be taken 
with a thermometer and an examination made for the 
other symptoms of fever (chill; irregularity of the sur- 
face temperature, especially of the extremities ; accelera- 
ation of the pulse and respiration, loss of appetite, depres- 
sion, albuminuria) . In cattle the increase in temperature 
as shown by the thermometer does not always correspond 
to the degi-ee of fever indicated by the other symptoms. 

When thoracic disease is suspected the chest wall 
should be percussed. Areas of hepatization and solidifi- 
cation may thus be discovered. The area of the lungs 
of cattle which can be percussed is limited, however, and 
imfortunately tubercular solidifications usually occur 
below this area. Percussion may reveal painful condi- 
tions of the lungs and pleura and may also produce 
cough. 



DAIRY INSPECTION 159 

If tuberculosis of the uterus is suspected, the sub- 
sacral, sublunibar and internal inguinal lymph-glands 
should be palpated per rectum. These glands are en- 
larged, firm, and often nodular when the uterus is tuber- 
culous. The mesenteric lymph-glands can also be 
examined in the same manner. 

Further information regarding internal conditions 
can be obtained by examining the sclerotic conjunctiva 
and the mucous membrane of the cheeks. These mem- 
branes are pale in tuberculosis and in other chi'onic debili- 
tating conditions which lead to ansemia and hydrsemia; 
bluish-red (cyanotic) in febrile, respiratory, and cardiac 
diseases and in conditions which interfere with the en- 
trance of air into the lungs ; brick-red to dark red, with 
the blood-vessels injected, in hypersemia and inflamma- 
tion of the brain and in conditions which interfere with the 
return of venous blood from the head to the heart ( pul- 
monary emphysema, organic heart disease and cardiac 
weakness) ; ecchj^motic in anthrax, severe ansemia and 
pernicious anaemia, and yellow in icterus. 

When symptoms suspicious of tuberculosis are 
present and no definite conclusion can be reached, the 
cow should be tested with tuberculin. 

When catarrhal mastitis is suspected and a definite 
diagnosis cannot be made, the milk should be examined 
by the catalase, leucocyte, or alcohol tests and micro- 
scopically, for streptococci. 

Ill STABLE PRACTICES 

Attention should be given to the manner in which the 
stable is cleaned, when and how the cows are cleaned, the 
methods of milking and of caring for the milk, the time 
of feeding, character of the feed, and when the litter is 
put down and the material used. 



160 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

1. Method of Cleaning the Stable, — If manure is 
allowed to collect in the stable the cows will become soiled 
and odors of decomposing manure and urine will per- 
meate the stable air and may be absorbed by the milk. 
The manure should be removed twice daily if possible, 
being taken out before each milking. It is necessary to 
complete this work at least an hour before the cows are 
milked in order to allow time for the air to become free 
from dust and odor before milking is begun. When the 
cows must be milked very early in the morning it is not 
always practicable to get the manure out of the stable 
an hour before milking time, and in such cases it is better 
to remove it after the cows are milked and fed. Milk of 
good quality can be produced under these conditions. If 
the manure is not hauled immediately to the fields, it 
should be stored as far away from the stable as possible. 
The stable and its immediate surroundings should be kept 
as free as possible from manure and other decaying or- 
ganic matter because flies breed in such material. House- 
flies may travel considerable distances from where they 
breed, flights of one-quarter to nearly a mile having been 
observed, but, as they seem to be attracted by odors, keep- 
ing the stable clean will in a measure serve as a protec- 
tion when flies are permitted to breed in the neighbor- 
hood. 

After the manure has been taken out, the litter on 
the rear end of the platform, which is usually soiled, 
should be swept into the gutter and given an opportunity 
to absorb any liquid which may be present. When the 
cows have been cleaned, the rear end of the platforms 
and the floor back of the gutter should be sprinkled with 
water and swept clean. In some stables the platforms 
and floors are again sprinkled after sweeping. This is 



DAIRY INSPECTION 161" 

done to keep the atmosphere as free from dust as possible. 
In other stables land plaster is spread in a thin layer on 
the floor and in the gutter to act as an absorbent. This 
is especially desirable when the floor is of wood or earth. 
The use of land plaster also seems to have the effect of 
reducing the number of flies. Although the inspector 
cannot be present during all of these operations, he can 
make a fairly accurate estimate of how thoroughly the 
work is done by observing the condition of the stable 
at the time of his visit. Dirt which has been permitted 
to remain for some time can be easily distinguished from 
fresh dirt. The wall in the rear of the cows and the 
corners formed where the walls, posts, and stall divisions 
join the floor should be especially examined. The pres- 
ence of cobwebs on the walls, ceiling, or other places is 
an evidence of infrequent sweeping. 

Flies. — The presence of flies in large numbers in and about 
a cow stable is objectionable for several reasons. The flies 
worry the cows and reduce the milk production, while the move- 
ments of the cows in their efforts to protect themselves from 
the insects interfere with milking and are also likely to dislodge 
dirt from the body of the cow; some of this dirt may fall into 
the milk pail. The common house-fly {Musca domestical is 
especially objectionable. It feeds upon all kinds of organic 
matter, including human excrement, and becomes contaminated 
with numerous bacteria. A single fly may carry over a million 
germs on the surface of its body. When it feeds upon milk 
or crawls or falls into milk vessels, many of these bacteria are 
transferred to the milk. Typhoid baciUi may be carried from 
infected fecal matter to milk in this way. The small, black cow- 
fly or horn-fly (Hematobia serrata, Lyperosia irritans L.) and 
the stable-fly or biting-fly {Stoinoxys calcitranis) disturb the 
cow more than the house-fly, because they are biting or blood- 
sucking insects ; but they do not as a rule invade the milk 
vessels or the milk. 
11 



162 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Various methods are used to reduce the number of flies in 
cow stables and in milk-houses. The cows are sprayed or 
brushed with mixtures of drugs or chemicals known as fly 
repellents. Sometimes sheets of fly-paper are placed about the 
buildings. Milk-houses are very often screened and more rarely 
stables are also screened. Fly repellents are only temporary 
in their action and they are often objectionable on account of 
their odor. Fly-paper is unsightly and inefficient. Fly-traps 
are more useful. Screening milk-houses gives good results and 
is desirable in all cases, but screening stables is not satisfactory. 
Since the doors must be opened frequently and sometimes for 
long periods to remove manure, to take in the feed, and to drive 
the cows in and out, there is abundant opportunity for flies 
to enter. The cow-fly or horn-fly is carried in on the cows. All 
of these methods are fundamentally defective because none of 
them prevents the breeding of flies. The most rational method 
of attacking the fly problem is to remove or abolish, in so far as 
is possible, the conditions which favor the development of the 
insects. To do this intelligently it is necessary to consider their 
habits and life history. 

Three varieties of flies are commonly found in cow stables: 
the common house-fly, the cow-fly or horn-fly, and the stable- 
fly or biting-fly. The house-fly and cow-fly are usually the most 
numerous, but in some sections of the country, especially in the 
grain belt, the stable-fly is present in large numbers. The dif- 
ferent varieties can usually be distinguished by the part of the 
cow which they occupy and by their sitting position. The small, 
black cow-fly is generally located upon the back and sides of the 
cow, and in rainy weather on the under parts of the body, sitting 
with the head downward. The stable-fly usually occupies the 
lower parts of the legs and nearly always sits with the head 
upward, while the house-fly may be found on any part of the 
cow and may sit in any position, but never with the head pressed 
into the hair as though feeding. The stable-fly is about the 
same size as the house-fly but has a more plump appearance 
and has longitudinal lines on the thorax and several dark spots 
on the abdomen. The horn-fly is smaller and black. 

The house-fly seems to prefer to deposit its eggs in horse 



DAIRY INSPECTION 163 

manure, but when this is not available tlie eggs are depo.sitecj. 
in other organic material. The heat generated by the decom- 
position processes which occur in such material hatches the 
larva; or maggots from the eggs in one day. The larva- develop 
into pupa; in 4 to 5 days and flies emerge 3 to 4 days later. The 
time from the affff to the fly is 8 to 10 days. 

It is recommended that manure be removed to the fields at 
intervals of seven days or less to prevent the development of 
the flies, but this plan will be effective only when the manure is 
stored in a receptacle wIjIcIj has a tiglit bottom, because the 
larva; or maggots frequently burrow into the earth to pujjate. 
The larvae also bury themselves in the same manner in an earth 
stable floor. This propensity of the larva; to migrate has been 
made use of to trap them by Hutchinson, who constructed a 
trap consisting of a raised platform with a shallow cement tank 
beneath it. The platform is made of wood strips 1^/4 inches 
thick and 1 inch wide, laid 1 inch apart. The manure is piled 
compactly on the platform, each day's addition being moistened 
with water. When the larva? are hatched they migrate down- 
ward and fall tlirough the spaces in the platforrrj into tlje water 
in the tank below, where they are drowned. 

Numerous experiments have been made to discover a sub- 
stance which when mixed with horse manure would destroy the 
larva; of the house-fly without affecting the fertilizing value 
of the manure. Naturally, the chemical fertilizers were tested, 
but it was found that acid phosphate and ground phosphate rock 
will not kill the larva;, while kainit (KCl and MgSO*) possesses 
only slight larva;cidal action. In several experiments. Cook and 
Hutchinson found that calcium cyanamid (CaCNg)? ^ substance 
frf:^juently incrjrporated in commercial fertilizers to furnish 
nitrogen, apparently destroyerl about 98 p<ir cent, of the larvae 
when applied to manure at the rate of Yj, P'^und to the bushel 
with an equal quantity of acid phosph>ate. The cost of this 
treatment is 1.8 cents per bushel of manure, but the fertilizing 
value of the manure is considerably increased, 'So that the actual 
cost is much less. A portion of the acid phosphate m^y be re- 
placed with kainit without affecting the larvaecidal effect and the 
mixture will then contain all the essential elements of plant food. 
Unfortunately, calcium cyanamid can be purchased only in car- 



164 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

load lots at the present time, but if a demand is created it will 
no doubt be available in smaller quantities. In the commercial 
fertilizers it is usually converted into urea, ammonia, etc. Of 
the various substances tested, the most satisfactory results were 
obtained with powdered hellebore and borax. One-half pound 
of powdered hellebore is mixed with 10 gallons of water and 
allowed to stand 24 hours. This quantity is sufficient to treat 
10 cubic feet (8 bushels) of manure, being applied with a 
sprinkler. The borax is applied with a flour-sifter, especially 
around the edges of the manure heap, and water is then sprinkled 
over it; about 1 ounce of borax and 2^ to 3 quarts of water 
are used to each cubic foot of manure. Floors, crevices, and refuse 
may be treated in the same manner with either hellebore or borax. 
Borax is perhaps a little more effective as a larvjecide than 
hellebore, but the latter is not at all injurious to the manure nor 
to crops while borax in excessive quantity interferes with plant 
growth. Manure treated with borax as above may be applied 
in any quantity up to 15 tons per acre without injuring the 
crops, except in the case of leguminous plants. When borax- 
treated manure is used to grow leguminous plants, it should be 
mixed with untreated manure. The effect of the repeated appli- 
cation of borax-treated manure has not been determined. The 
cost of treating manure with powdered hellebore is a little over 
y2 cent per bushel, while the expense of the borax treatment 
is a little less than ^^ cent per bushel. 

The cow-jly or horn-jiy lays its eggs in fresh cow manure. 
The larv£e are hatched in 24 hours and develop into pupse in 5 
days. The pupag burrow into the ground and flies emerge in 8 
days, the time from the egg to the fly being 14 days. 

These flies feed upon the blood of the cow and are therefore 
not likely to get into the milk or milk vessels. In biting through 
the skin of the cow to obtain food, they cause the animal con- 
siderable discomfort. When driven off the body of the cow, they 
fly only a short distance away and then immediately return, so 
that, while feeding, they are a continual torment. 

Fly repellents are used to protect the cow from the attacks 
of these insects. A mixture of one part of oil of tar and nine 
parts of cotton-seed oil or crude Beaumont oil, applied daily 



DAIRY INSPECTION 165 

with a spray pump or syringe, is an effective and safe repellent. 
The following mixture, it is claimed, will act effectively for one 
week: Soap, 1 pound; water, 4 gallons; crude petroleum, 1 
gallon, and powdered naphthalene, 4 ounces. The soap is shaved 
into thin slices and dissolved in the water by heating; the 
naphthalene is dissolved in the crude oil. The two solu- 
tions are mixed by stirring vigorously or churning for 15 
minutes. The mixture is stirred thoroughly each time before 
using and is applied to the cows with a brush once or twice 
weekly. While fly repellents afford the cow temporary relief 
from the biting flies, they are of no value in the control or 
eradication of the flies. Hellebore and borax have not been 
tested on the larvas of the cow-fly, but it is very probable that 
they would be as destructive to these larvae as to those of the 
house-fly. 

When cows are kept in the stable, with occasional liberty 
in an exercise yard, the breeding of cow-flies can be prevented 
by removing the manure from the stable and yard to the fields 
daily, or if it is stored in the vicinity of the stable, by removing 
it to the fields at intervals of not less than 12 days, provided 
the floor of the stable and the floor of the dung-stead are so 
constructed that the pupse cannot burrow into the ground. 
When cows are pastured it is not practicable to control the 
breeding of cow-flies. The manure dropped in the pasture fur- 
nishes ideal breeding conditions. When the flies emerge they 
take up a position on the body of the cow, where they feed and 
rest, and are carried into the stable by the cow. 

The stahle-fLy breeds in horse manure and in decaying grass 
and straw heaps ; also in cow droppings which have become dry 
and disintegrated, and in ensilage. Eggs deposited in these 
substances hatch out larvge in 1 to 3 days. The larvae develop 
into pupas in 11 to 30 days or more, and the flies emerge in 
6 to 20 days, the time from the egg to the fly being 18 to 53 
days and upwards. The stable-fly feeds on the blood of cows 
and other domestic animals, and also bites man. Unlike the 
house-fly, it is not likely to infect milk with bacteria, since it 
does not feed upon that substance. 



166 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

2. Cleaning the Cows. — The body surface of the cow 
may be soiled with dirt and manure when the animal lies 
down, dust settles on the skin from the air, and dead 
epidermal cells and hair are cast off from the skin. This 
material is very rich in bacteria and, if not removed, some 
of it will be dislodged during milking and may fall into 
the milk pail. The manure contains numerous gas-form- 
ing and putrefactive bacteria and is therefore especially 
objectionable. Dry dirt and manure should be loosened 
with a curry-comb and then brushed out with a stiff brush, 
which will also remove loose hairs and epidermal cells. 
If the dirt or manure is not dry it must be washed off with 
a clean cloth and water. The addition of 1 to 2 per cent, 
of washing soda (a Mason jar lid full to a 12 quart 
bucket) is of great assistance. White hair is likely to 
show a stain after the dirt has been washed off and this 
must not be mistaken for dirt. "No dust can be rubbed 
out of an area that is only stained. In cleaning the cows 
special attention should be given to the udder, flanks, 
external surface of the thighs and the switch. In some 
dairies the switch is washed at short intervals. Keeping 
the hair clipped short on these parts and on the buttocks 
will facilitate the work of cleaning. It is advisable to 
have the switch clear the ground by about 4 inches, but 
there is some objection to cutting the switch of pure-bred 
cows. 

After the udder has been brushed dry it should be 
wiped with a damp cloth. The cloth and water should be 
clean at the start and the water should be changed as 
soon as it becomes soiled. Ordinarily, a bucket of clean 
water is required for every eight cows. In high-class 
dairies a small damp towel is used for each cow; each 
towel is used only once and is then washed and sterilized. 



DAIRY INSPECTION 167 

The brushing should be finished a half hour before milk- 
ing, to allow time for the dust to settle from the air of 
the stable, but the udder should be wiped just before 
milking is begun. If the udder is brushed inmiediately 
before milking the number of bacteria in the milk will 
be about doubled. The practice indulged in by some 
milkers of attempting to clean the udder by wiping it 
with the hand after sitting down to milk is not a good 
one, as it dislodges a lot of loose hair, epithelial cells and 
particles of dirt which may fall into the milk pail. The 
purpose in wiping the udder with a damp cloth is to 
moisten any loose dirt, hair, etc., that may remain after 
brushing and thus prevent these particles from falling 
into the milk. 

The number of bacteria dislodged from apparently 
clean udders by the process of milking is reduced about 
two-thirds by dampening the surface of the udder. Too 
much water should not be used, as any excess will run 
off the end of the teat and may drop into the milk pail, 
while, in winter, the exposure of a wet udder to cold air 
is very likely to cause congestion and cracking of the 
skin, especially at the base of the teats and on the teats, 
and may also cause catarrhal mastitis. Washing the 
udder, unless it is afterward rubbed dry, is not as effective 
in keeping dirt and bacteria out of milk as is wiping it 
with a damp cloth after dry brushing. The best results 
are obtained by wiping the udder with a cloth dampened 
with a 2 per cent, solution of washing soda after it has 
been cleaned by brushing, and then anointing it with a 
small quantity of vaseline. As much vaseline as can be 
taken up on the end of the finger is rubbed over the 
palms of the hands, which are then passed lightly over 
the udder. This method takes less time than washing 



168 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

the udder, while the skin covering the teats remains soft 
and pliable and there is an entire absence of cracks and 
sores, even in winter. 

It is sometimes stated that dampening or washing the 
udder irritates the skin, causing it to swell and crack, and 
that it decreases the milk flow, but this is not entirely 
correct. The udder will suffer no in j ury whatever unless 
too much water is used and the organ is exposed to cold 
air in a wet condition. There may be a decrease in the 
milk secretion when a cow is subjected to the process 
for the first time, but the milk flow returns to normal in 
a few days and very frequently it is increased. The mas- 
sage which accompanies the brushing and the wiping or 
washing favors the flow of blood to the udder and usually 
increases the secretion of milk. Udders which are kept 
clean are affected with disease less frequently than dirty 
udders. 

As a general rule, cows will produce more milk when 
kept clean and comfortable than when they are kept 
otherwise. Therefore cleaning the cows not only assists 
in keeping dirt and bacteria out of the milk but usually 
also increases the milk production. After the cows have 
been cleaned they should be fastened so that they cannot 
lie down before they are milked. 

3. Methods of Milking. — The condition of the milker 
as regards health and cleanliness should receive the atten- 
tion of the inspector. No one should be permitted to 
milk cows or handle milk in any way who is affected with 
any infectious disease, especially typhoid fever, diph- 
theria, and scarlet fever, or who has been in contact with 
persons affected with any of these diseases. Persons 
affected with tuberculosis, syphilis, severe diarrhoea, 
suppurating sores on exposed surfaces, or any throat 



DAIRY INSPECTION 169 

disease should also be debarred from employment on a 
dairy farm. 

The milker should have special clothing to wear while 
milking. Considerable dust and dirt collects on the outer 
surface of clothing worn while cleaning the cows and 
stable or in doing farm work, especially if it is made of 
material with a soft, rough finish, and a good deal of this 
dirt may di'op off into the milk pail during milking. A 
clean blouse, overalls, and a cap should therefore be put 
on before beginning to milk. These should be made of 
washable material with a smooth, hard, finish like duck, 
linen, or drilling. White linen or duck is best. One or 
two suits a week in winter and two or three in summer 
will be required in order to have a reasonably clean suit 
at all times. An apron or a pair of overalls with a bib 
is sometimes used because they are easier to put on and 
off; but they do not cover the shoulders and arms, the 
parts from which dirt is most likely to be dislodged in 
milking. 

Before beginning to milk, the milker should wash his 
hands thoroughly, using soap, water and a nail brush, and 
dr}^ them carefully with a clean towel. After doing so, 
he should not touch anything but the teats of the cow, 
milk pail, and milk stool. The inspector should note 
what facilities are provided for washing and drying the 
hands. 

When the milking of a cow is finished, the pail should 
be carried to the weigh room and the milk weighed and 
emptied, the weight of the milk being recorded on the 
milk record opposite the name or number of the cow. In 
passing in the rear of the cows, the milk pail should be 
carried on the side of the body furthest away from the 
cows ; covered- top pails should be carried with the open- 



170 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

ing on the opposite side from the body. This will protect 
the milk from contamination by cows switching the tail, 
splashing of manure or urine, and dirt falling from the 
clothing of the milker. The milker should wash his hands 
again before milking another cow and should dry them 
well on a clean towel. Small, individual towels, about 
10 X 10 inches, which can be used once and then thrown 
aside for washing, are much more desirable than a large 
towel used in common by several milkers. 

Soiled hands are a prolific source of bacteria in milk. 
As many as 45,000,000 bacteria have been found on one 
hand of a farm laborer. Washing and drying the hands 
will reduce the number of bacteria 75 per cent, or more, 
and also decrease the danger from chronic typhoid bacilli 
carriers. Experiments indicate that careful drying is 
quite as important as thorough washing, fewer organisms 
remaining after careful drying than when the hands are 
rinsed in an antiseptic solution after washing and are not 
carefully dried. 

Milking should be done with dry hands. When the 
hands are wet the moisture assists in loosening the epi- 
dermal cells and dirt from the surface of the teat, and this 
material gradually moves down to the end of the teat 
and drops off into the milk pail. The practice of wetting 
the hands with milk when beginning to milk is to be con- 
demned because this milk, after being mixed with the 
dirt on the teats, drops off into the pail. 

Sometimes dairymen claim that it is sufficient to wash 
the hands before beginning to milk, saying that if the 
udders are clean the hands will not become soiled. This 
would be true if the udders were bacteriologically clean 
and if the milker did not touch anything but the clean 
teats of the udder. But the milker sometimes touches 



DAIRY INSPECTION 171 

other parts of the cow in pushing or striking the animal 
to cause it to stand over in the stall and in protecting 
himself against a switching tail. In addition, the milk 
bucket is often rested on the floor and the bottom subse- 
quently grasped in emptying it, thus soiling the fingers 
with material from the floor. The milking stool may be 
another source of contamination for the hands. It should 



Fio. 13. — Open or uncovered pail. Fia. 14. — Covered-top pail with opening 

nearly iiorizontal (with strainer attached) . 

therefore be kept clean and it is best to use one made of 
metal. 

The milk should be drawn without jerking the teats, 
as this dislodges dirt and bacteria which are liable to fall 
into the milk. " Stripping " the teats is also objection- 
able for the same reason. The first few streams of milk 
(fore-milk) from each quarter should be drawn into a 
separate vessel, as this milk washes out the milk cistern 
and teat canal and contains a greater number of bacteria 
than the milk subsequently drawn from the udder. The 



172 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



fore-milk from a normal udder usually contains from 
to 500 bacteria per c.c, mostly udder cocci. Sometimes 
more may be present, but when the number exceeds 
5000 per c.c. the udder is infested with mastitis organ- 
isms, usually streptococci. The fore-milk should not be 
milked out upon the floor or litter as this supplies condi- 
tions which are favorable to the growth of bacteria. 

The type of milk pail has a 
very pronounced influence on the 
bacterial content of milk. The 
larger and more horizontal the 
opening of the pail the greater the 
opportunity for contamination. 
There are two types : The open or 
uncovered pail and the covered-top 
pail (Figs. 13, 14, and 15). The 
top of the open pail is entirely im- 
protected and is about 12 inches in 
diameter, while the covered-top 
pail has an opening only 7 inches 
in diameter, the remainder of the 
top being covered. The smaller 
opening, of course, offers much less 
opportunity for dirt to fall into the 
milk. It is more difficult to milk 
into the covered-top pail than into the open pail, especi- 
ally at first, but this is largely overcome by practice. 
There are two varieties of covered-top pails: One with 
the opening vertical and protected by a hood and the 
other with the opening more or less horizontal (Figs. 
14 and 15) . The pail with the vertical opening is prob- 
ably somewhat more difficult to milk into than the pail 
with the horizontal opening, but it affords a much greater 




Fig. 15. — Covered-top pail with 
vertical opening. 



DAIRY INSPECTION 



173 



protection against the contamination of the milk than the 
pail with the horizontal opening, even when the latter 
contains a cheese-cloth and wire-gauze strainer. Some 
varieties of pails in which strainers are used have a spout 
on the side so that they can be emptied without removing 
the strainer. There is one type of pail which has no 
opening in the top, but a spout extending from the side 




Fig. 16. — Another variety of covered-top pail._ The milker Bits on the pail and milks into 
the funnel, which is covered with a cheese-cloth strainer. 

has a funnel in the end to receive the milk. The milker 
sits on the pail and milks into the funnel. When the pail 
is to be emptied the funnel is removed and the milk is 
poured out of the spout. Pails with several parts are 
not as easily kept clean as the other kind. Every addi- 
tional piece of apparatus not only increases the work of 
cleaning but also provides another possible medium for 
the conveyance of bacteria to milk. 

Strainers of cheese cloth and wire gauze cannot be 



174 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

depended upon to protect milk from contamination. 
They do not keep out bacteria, but hold back only the 
larger particles of dirt. Some of these particles are sub- 
sequently dissolved by milk and carried through the 
strainer, while bacteria are washed off of the insoluble 
particles remaining on the strainer. It is also difficult 
to clean strainers of this kind thoroughly. Particles of 
dirt become entangled in the meshes of the wire gauze, 
especially at the periphery where it is soldered to the tin, 
and it is difficult to remove them, while the cheese cloth 
requires much care in cleaning. It should be rinsed in 
cold water, washed in hot water containing two per cent, 
of soda, again rinsed in cold water and then wrapped in 
a clean cloth and sterilized in a steam chest. If a steam 
chest is not available, it should be put into a thick paper 
sack and placed in a stove oven and kept there until the 
sack begins to scorch. A strainer composed of a thin 
layer of absorbent cotton is much more effective and it 
can be tlirown away after being used and thus save the 
labor of cleaning. Some of the bacteria are apparently 
enmeshed in the cotton and kept out of the milk. The 
use of a cotton strainer has reduced the bacterial content 
of the milk nearly one-third in some tests. Coarse cot- 
ton-flannel and turkish toweling are also used for strain- 
ers, but they are no more effective than cheese cloth. 

Bacteria cannot be kept out of milk by strainers nor 
can they be removed by these contrivances after they 
have entered the milk. The coarse particles of dirt may 
be strained out, but the most objectionable part of the 
dirt the bacteria, will remain. Much more satisfactory 
results will be obtained by cleanliness and care in milking 
and in the subsequent handling of the milk. 

In some receiving stations and distributing plants. 



DAIRY INSPECTION 175 

milk is run through a machine known as a clarifier, in 
which the milk is centrifugalized and the heavier sub- 
stances, such as dirt particles, cells, and some of the bac- 
teria, separated from it. The process is known as clari- 
fication. When determined by the plate method, the 
number of bacteria is frequently greater after clarifica- 
tion than before, but this increase is probably due to the 
breaking up of clumps of organisms by the centrifugali- 
zation. Some of the bacteria are removed from the milk 
since the sludge or residue remaining in the clarifier 
contains bacteria in considerable numbers. The per- 
centage removed cannot be very great, however, because 
the milk is exposed to the separating action for only a 
short time. The sludge or residue is composed very 
largely of the amorphous substances normally present in 
milk, the remainder consisting of bacteria, cells, hair, and 
particles of dirt. If clarified milk is subsequently centri- 
fugalized for three minutes at 3000 revolutions per min- 
ute, sediment will be deposited, showing that all of the 
sediment is not removed by clarification. All gross sus- 
pended dirt, such as hairs, dust particles, etc., are, how- 
ever, removed by the clarifier, and for this purpose it has 
many advantages over strainers. But milk containing 
pathogenic organisms is no cleaner from a hygienic 
standpoint after clarification than before (Bahlman, 
Hanomer). 

4. Feeding. — The cows should not be fed immedi- 
ately before milking. When hay or other dry fodder 
is brought into the stable and distributed around among 
the cows, more or less dust is liberated. This dust con- 
tains numbers of bacteria, principally peptonizers, and 
if milking is done while it is floating about in the stable 
air some of these organisms will get into the milk. If 



176 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

the hay or fodder is thrown down directly into the stable 
from a loft above, the quantity of dust set free in the 
stable air is much greater than when it is throvni down 
into a passageway outside of the stable. Feeding meal 
or ground grain immediately before milking is also objec- 
tionable, and for the same reason. It is not necessary to 
feed cows before milking to keep them quiet during milk- 
ing; they soon become accustomed to being fed after 
milking. 

The investigations of Ruehle and Kulp^ indicate that 
under ordinary conditions dust in the stable air is not 
nearly as much concerned in the bacterial contamination 
of milk as has been generally believed, but as it is only 
necessary to perform the several stable operations in a 
certain order, and does not require additional labor, to 
protect milk against this source of contamination it is 
advisable to take this precaution, especially since un- 
usual conditions which will increase the infection from 
this source are likely to prevail at times. 

The feeding of ensilage fills the air of the stable for 
a time with the odor characteristic of this substance, and 
if milking is done during this period the odor and taste 
of the milk is likely to be tainted. This is likewise true of 
cabbage and rape, and also of beets, turnips, rutabagas 
and carrots, and their tops (see page 29) . Odors in the 
stable are very quickly absorbed by milk, especially when 
it is warm. 

Sudden changes of feed and overfeeding should be 
avoided. A sudden change from dry to green feed will 
produce diarrhoea. Old and highly acid ensilage and 
sometimes overfeeding will have the same effect. Indi- 

1 Geneva, N. Y., Expt. Sta. Bull. No. 409. 



DAIRY INSPECTION 177 

vidual milk from cows in this condition contains prop- 
erties which cause digestive and intestinal disturbances 
in infants ; when sufficiently diluted with milk from cows 
in normal condition, it is not likely to have this effect. 
The presence of diarrhoea also increases the difficulty of 
producing clean milk. No grain, meal, or fodder that 
is musty, mouldy, or otherwise unsound should be fed 
to milch cows. Diarrhoea has been observed in persons 
ingesting milk from cows receiving feed of this kind. It 
has been assumed that the diarrhoea was due to substances 
formed in the feed being excreted in the milk, but it is 
possible that in such cases the fungi or bacteria responsi- 
ble for the change in the feed pass directly from the feed 
to the milk after it is drawn from the udder and bring 
about decomposition changes. The use of distillery waste 
or slop and of wet brewers' grains is prohibited by law 
in some sections. These substances when fed fresh in 
moderate quantity have no injurious effect upon the 
milk, but when they are fed in an advanced stage of 
fermentation or putrefaction the milk may cause diges- 
tive disturbances, especially in babies, and the manure 
of the cows has a bad odor and is very soft. In addi- 
tion, when these substances are fed it is difficult to keep 
the stable clean and free from bad odors, especially the 
mangers and storage bins or pits. Particles of the feed 
remain in corners and crevices and decompose, produc- 
ing a foul odor. On the other hand, dried distillers' grains 
and dried brewers' grains are entirely wholesome feeds. 
It is advisable to water the cows at least twice daily. 
Whether the water is given before or after feeding is 
of no consequence, but it is important that a sufficient 
quantity be given. The greater the milk production, 
the more water required. 
12 



178 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

5. Bedding. — Bedding or litter assists in keeping 
the cow clean and affords some protection against a hard, 
cold floor ; it also assists in keeping floors clean and dry, 
especially those of wood and earth, by absorbing the 
liquid manure. Actual test has shown that when beef 
cattle are well-bedded they lie down more frequently 
and for longer periods and make a greater gain in weight 
in proportion to the feed consumed than they do under 
less comfortable conditions, and it is reasonable to assume 
that dairy cows are aiTected in a similar manner. 

The materials usually used for bedding are wheat 
straw, shredded corn fodder, shavings, and sawdust. 
From a hygienic standpoint, shavings and sawdust are 
the most satisfactory. They keep the cows cleaner and 
are less dusty than shredded corn fodder or straw, but 
they decay more slowly and are not as satisfactory in 
supplying humus to the soil. Shredded corn fodder and 
straw are about equally dusty, but the cows can be kept 
cleaner with the former. Cut straw is less satisfactory 
than uncut. Shredded corn fodder excells all of the 
others in absorbing liquids, with shavings next in order, 
then straw, and finally sawdust. The low absorption 
power of sawdust is due to the fact that it is usually 
damp from exposure to rain. Sawdust is the cheapest 
material for bedding in localities where it is available. 
Where there is a convenient market for corn fodder 
and straw, or where the fodder can be used for feed, it 
will pay to buy shavings for bedding. 

All bedding material, except sawdust when it is 
damp, being more or less dusty, should be put down 
in the stable after the milking has been completed. This 
is especially necessary when corn fodder or straw is used, 
as the dust in these is likely to contain large numbers 



DAIRY INSPECTION 179 

of peptonizing bacteria. Mouldy or musty straw is ob- 
jectionable because it contains bacteria and fungi which 
aifect the keeping qualities and wholesomeness of the 
milk. 

The time required to perform the various stable prac- 
tices described in the preceding pages is of importance 
to the milk producer, and the inspector should there- 
fore be familiar with this side of the subject. The fol- 
lowing figures were obtained from the manager of a 
large and successful dairy farm and represent the aver- 
age time required by different men to perform each 
operation, the men being timed without their knowl- 
edge : Taking up manure, % minute for each cow 4 times 
daily. 

Sweeping platforms, stable floor, and feed troughs, 
and wiping stanchions, IV2 minutes for each cow twice 
daily. 

Grooming, 2^^ minutes for each cow twice daily. 

Washing flanks and tails, % minute for each cow 
twice daily. 

Washing udders, two waters, % minute for each cow 
twice daily. 

Drying udders and drawing fore-milk, % minute 
for each cow twice daily. 

Bedding, % minute for each cow twice daily. 

Feeding, II/2 minutes each cow twice daily. 

Total time per cow, about 8% minutes twice daily. 

IV. MILK HOUSE 

On every farm where milk is produced there should 
be a special room or compartment to which the milk 
can be removed immediately after it is drawn from the 
cow and where it can be subjected to some method of 



180 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

cooling. When the milk from the individual cows is 
emptied into a shipping can in the stable, it is exposed 
to contamination by any dust or odors which may be 
present in the stable air, and, furthermore, it is not likely 
to be promptly cooled. A milk room is therefore a neces- 
sity. On dairy farms it has been found to be convenient 
as well as economical to have this room in the same build- 
ing with other rooms in which the utensils and vessels 
can be washed and in which the milk can be stored. A 
building of this kind is called a milk house or dairy build- 
ing and sometimes also contains a room in which the 
milk is bottled. A spring house may, when the condi- 
tions are suitable, serve as a substitute for a storage room 
or refrigerator, but the practice of washing the milk ves- 
sels in the kitchen of the dairyman's residence is very 
objectionable. The milk house should be arranged so 
that it will not be necessary for the milkers to enter the 
room in which the cooler is located or to pass through 
the wash room to empty their milk pails. This will 
greatly reduce the labor of keeping the several rooms 
clean. The floor plan of a milk house in which this idea 
is carried out is shown in Fig. 17. The milkers pass 
from the stable to the weigh room, where the milk, after 
being weighed, is emptied into a tank, from which it 
is carried by a short pipe passing through the wall to the 
reservoir on top of the milk cooler. 

The inspector should observe the location of the milk 
room or milk house and the materials of which it is con- 
stiaicted ; note the provisions for cooling the milk ; exam- 
ine the condition of the apparatus and utensils and the 
facilities for washing and cleaning them, and investigate 
the source of the water used for the latter purpose. 

1 . Location. — The milk house should be isolated from 



DAIRY INSPECTION 



181 



driveways, in so far as this is possible, and there should 
be an open-air space between it and the stable. If the 
milk room is not entirely separated from the stable, the 
chief object of having it, namely, to protect the milk 
from the stable air, will be defeated. If the surrounding 
grounds are dusty or if much-used dirt roads are close 
to it, the atmosphere in the building will be dusty. Some 




FlGn7.^ — Floor plan of a conveniently arranged milk honee. A, receiving funnel; B, 
milk cooler; C, bottle filler; D, refrigerator; E, cooling tank; F, sterilizer; G, Babcock 
tester; H, bottle washer; I, concrete sink; J, boiler; K, chimney; L, floor drains; M, 
sunning rack; N, separator. (Hoard's Dairyman). 

system of drainage is necessary to carry off waste water 
and washings, otherwise the air may become foul from 
decomposing milk. 

2. Construction. — On entering the milk house, the 
inspector should first note the odor of the air. A sour 
or putrid odor indicates uncleanliness or defective drains. 
A musty or mouldy odor results from lack of ventilation. 
The floor, walls, and ceiling should be examined, the 
material of which they are constructed and their condi- 



182 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

tion in regard to cleanliness being noted. Cement is the 
best material because it can be most readily cleaned, but 
smooth boards with tight joints, oiled or painted, will 
do fairly well for the walls and ceiling, although it is 
desirable to have the walls finished in cement for about 
four feet above the floor, especially in the room used 
for washing the milk vessels and utensils. The floor 
should always be constructed of cement. The lighting 
should also be observed. There should be a sufficient 
number of windows to furnish good light, and some good 
method of artificial lighting is also desirable. All win- 
dows and doors should be screened against flies. 

3. Apparatus, — The apparatus present in the milk 
house and its condition should be observed. There ought 
to be some means of cooling the milk and keeping it 
cool, and there should be facilities for cleaning the milk 
vessels and utensils, including a convenient and plenti- 
ful supply of hot and cold water. If the milk is bottled, 
a bottle washer, bottle filler, and bottle capper should 
be provided. These need not necessarily be expensive. 
A sterilizer is also desirable. It is a protection against 
the contamination of the milk through returned bottles 
and it is also a great aid in keeping the milk vessels and 
utensils clean. A bottle filler and capper will guard 
the milk against contamination by the fingers. 

A cooler, sometimes called an aerator, is necessary 
for the rapid cooling of milk. This apparatus is con- 
structed so that the milk flows in a thin layer over a 
sheet of tinned metal while cold water or brine flows 
on the other side of the metallic sheet and absorbs heat 
from the milk. There are four types of milk coolers: 
(a) conical, ( h) corrugated, (c) tubular, and (d) inter- 
nal or double-tube. 



DAIRY INSPECTION 



183 



(a) The conical cooler (Fig. 18) is a cone-shaped 
tank with a gutter around the base and a movable reser- 
voir at the top. The reservoir has small perforations 
in the bottom around the periphery. When the cooler 
is in use, the cavity of the tank is filled with water or 
ice water. The milk is poured into the reservoir and, 
passing out through the perforations, flows in a thin layer 
down over the external surface of the conical tank, col- 
lecting in the gutter at the bottom. From the gutter 
it is permitted to run into the shipping can or bottler. 





— , /■ AGITATOR 

\ MILK r/l 
\ RECEIVER / )-j-\JQmiKT\tiG T\iBE. 


PeftFORATIONS. 


•' ^p- 7Zl:3"^"--PERFORATIONS 




/ _pv,-jjr - - - -\ — OVFRFI nw PIPE 




fi^^^^^^^^^ FOR water" 


COOLING DRUM- 


"l^^^^^A, 


TROUGH TO /! 
COtLECTMllK j| 


^^A 


INLET PIPE- s-HB 
POR WATER -^-^ 


^^^S==-=^^^C^^tIZPUTLEr PIPE 




Fia. 18. — Cooler of conical type. 

One model of this type of cooler has attachments 
for pipe or hose to carry cold water into the tank and 
to remove the water which has been warmed by the heat 
absorbed from the milk; another which is intended for 
use on farms without a water pipe system does not have 
these attachments, and the warm water must be removed 
and the cold water added with a dipper or similar vessel. 

( b ) The corrugated type ( Fig. 19 ) of cooler consists 
of two sheets of corrugated copper, with a small water- 
tight space between them and tinned on the outer sur- 
face. The cooling fluid enters through a pipe at the 



184 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

lower part of this space and discharges at the top. The 
milk is poured into a reservoir or tank at the top of 
the corrugated metallic sheets and, passing out through 
perforations in the bottom of the reservoir, flows slowly 
downward in a thin layer over the corrugated surfaces 
to a trough at the bottom, from which it passes into the 




Fig. 19. — Corrugated type of cooler. 



collecting can or bottling apparatus. A late model of 
the corrugated type of cooler is conical in form and is 
provided with a metal cover to protect the milk from 
contamination while it is passing over the cooling sur- 
face. 

(c) The tubular cooler (Fig. 20) consists of a num- 
ber of pipes arranged horizontally, one under the other 



DAIRY INSPECTION 



185 



and close together. They are connected at either end 
so that fluid can flow from one tube into another. The 
coohng fluid enters the bottom pipe and flows upward 
through the various pipes, while the milk flows down- 
ward over the outer surface of the pipes from a reservoir 




Fia. 20. — Tubular cooler, with continuous surface. 

at the top and is received in a collecting tank at the 
bottom. In some coolers of this type the pipes can be 
taken out to be cleaned and sterilized. Sometimes these 
coolers are arranged for ice water to run through the 
lower pipes and water through the upper pipes, the 
object being to save ice. The corrugated coolers have 
an ice-water section which can be attached to the bottom. 



186 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

(d) The internal or double-tube cooler (Fig. 21) 
is a system of double pipes, one within the other. The 
milk flows through the inner pipes and the cooling fluid 
through the outer. In this type of cooler the milk is 
protected from possible contamination from the air. To 
facilitate cleaning, the connections between the individual 
pipes are removable (detachable return bends). 

With a cooler, the temperature of milk can be low- 
ered to within a few degrees of the cooling fluid in a 
few minutes, provided the apparatus is not pushed be- 
yond its capacity. If the cooler is not large enough, 
the milk is likely to be permitted to flow over the cooling 
surface too rapidly for much of the heat to be absorbed 
by the cooling fluid. The size of the cooler required 
will depend on the quantity of milk to be cooled and 
the number of milkers. The capacity of coolers as stated 
by manufacturers is usually based on 20 square feet of 
cooling surface per 1000 pounds of milk. 

Milk should be cooled to as low a temperature as 
possible, and should be kept cool. The lower the tem- 
perature, the slower the bacterial growth and the longer 
the milk will keep in good condition (see page 43). 
Above 60° F. the bacteria multiply rapidly, and at 70° 
F. or above growth is not only very rapid, but the de- 
velopment of the more objectionable bacteria is favored. 
When well water or spring water is used for the cooling 
fluid, the temperature of the milk cannot be reduced 
much below 60° F. and often not that low. The tem- 
perature of well and spring water in the section around 
Philadelphia ranges from 52 to 55° F. in the spring 
and summer months, but in the late summer and early 
fall it is usually higher, especially in sandy regions, rising 
to 69 and 70° F. in some sections. With ice water, the 




Fig. 21. — Internal or double-tube cooler. 



DAIRY INSPECTION 187 

milk can be cooled down to 40° F., while with ammonia 
or brine it can be brought still lower, even to freezing.^ 
The cooler must be thoroughly cleaned each time it 
is used, stored in a clean place, and protected from dust 
while in operation, or the milk will take up large num- 
bers of bacteria during the process of cooling. When the 
cooler is not properly used and cared for, it has been 
found that better results can be obtained by pouring the 
milk directly into a shipping can and placing the can 
in cold water, although the temperature is lowered very 
slowly under these conditions, three to four hours being 
required for the temperature to fall to 60° F. In some 
cases it has been found more satisfactory to have the 
milk taken in cans to the shipping station and to cool 
it there. When this plan is followed the milk must 
reach the shipping station during the period the germi- 

* In the northern part of the United States, about 1^ tons 
of ice will be required each year to cool the milk obtained from 
each cow, while in the southern states about 2 tons will be 
necessary, allowing for the waste by melting. A ton of packed 
ice will occupy 40 to 50 cubic feet of space; 12 inches should 
be allowed on the sides and bottom for sawdust or other pack- 
ing material and 3 to 4 feet on top for packing and ventilation. 
With these figures, the dimensions of an ice house of any ca- 
pacity desired can be determined. A foot of packing material 
should be placed under the ice even when the ice house has 
an earth floor, earth being a fairly good conductor of heat, 
especially when wet. Water from the melted ice will usually 
drain off through the soil unless the latter is of clay, in which 
case it will be necessary to excavate 1 or 2 feet, put in a tile 
drain, and fill in with gravel or cinders. The pipe supplying 
water to the milk cooler may be run under the floor of the ice 
house with advantage. (A number of good plans for building 
ice houses will be found in the U. S. Department of Agriculture 
Farmers' Bulletin No. 623.) 



188 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

cidal power is active (see page 43). As a general rule, 
however, it is best to run the milk over a cooler immedi- 
ately after it is drawn from the cow. When the milk 
is emptied from the milk pail directly into the tank of the 
cooler and passes from the cooler into a bottling machine, 
it is important to milk the cows in such order that milk 
of low fat per cent, and milk of higher fat per cent, 
will be mixed in passing through the bottling machine. 

After being cooled, the milk should be stored in a 
cool place, such as a refrigerator, ice-water tank, or 
spring house, until sent to the railroad station. The in- 
spector should note the facilities provided for this pur- 
pose. Milk can be kept cooler in a tank of ice water 
than in a compartment in which the air is cooled by ice, 
unless the latter is well insulated. The temperature 
of air in an ice-cooled refrigerator is usually not much 
below 50° F., whereas the temperature of water in which 
ice is floating is generally as low as 40° F., and often 
lower. 

While being hauled to the station, the milk should be 
protected from the heat in summer. This is usually 
done by covering the cans with a woolen blanket. A 
wet blanket is more effective than a dry one. Jackets 
of hair enclosed in canvas are sometimes used to cover 
the cans. Ice in small pieces should be placed in the 
boxes in which bottled milk is shipped. 

The surface of the milk cooler and the inner sur- 
face of all milk vessels should be examined for cleanli- 
ness, rusted areas, and open seams. Uncleanliness is 
indicated by an odor of sour or putrid milk and by the 
presence of particles of coagulated milk. These parti- 
cles may be very small, sometimes no larger than a pin's 
head. All surfaces with which milk comes in contact 



DAIRY INSPECTION 189 

should be covered with tin. Rusted areas are rough 
and are not easily cleaned, and they sometimes give the 
milk a "fishy" taste. Milk stored in rusted vessels will 
acquire a bitter, astringent taste if it becomes very acid, 
in consequence of the formation of iron lactate by the 
combination of the lactic acid with the iron. The most 
common location of rust is in the seams and joints, espe- 
cially in the joint between the bottom and sides. All 
seams should be filled flush and smooth with solder. 
Seamless vessels are best. The use of galvanized iron 
buckets for milk pails should not be permitted. 

Inquiry should be made in regard to the method 
of cleaning the utensils and vessels, including bottles, 
and the facilities provided for this purpose should be 
noted. The utensils and vessels should be first rinsed 
with cold or lukewarm water. If hot water is used first, 
it will coagulate the albuminous substances in the milk 
and cause them to stick to the inner surface of the vessels, 
to the surface of the milk cooler, etc. After rinsing, they 
should be washed in hot water containing washing soda 
or soap powder and then rinsed again in hot water. The 
brushes used in cleaning should be boiled for ten min- 
utes each time after they are used; they should be of 
good quality so that the bristles will not come out. The 
last rinsing ought to be thorough, to insure the removal 
of all the washing powder, otherwise the milk may have 
a "fishy" taste. 

Unclean milk vessels and utensils are one of the most 
prolific sources of bacteria in milk. Particles of milk 
form an excellent culture media for bacterial growth, 
while the water used to wash the apparatus, the milk 
itself, and the air furnish the organisms necessary to 
start the growth. The greater proportion of the organ- 



190 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

isms are lactic acid and putrefactive bacteria. Even 
when the vessels and utensils are thoroughly cleansed 
in the manner described, they still contain bacteria. To 
reduce contamination of milk from this source to the 
minimum, sterilization is necessary in addition to thor- 
ough washing. The effects of sterilization are illustrated 
by the investigations of Prucha, Harding, and Weeter, 
who found that the same milk which contained 515,203 
bacteria per c.c. when the vessels and utensils were 
washed but not sterilized contained only 3875 per c.c. 
when the apparatus was sterilized after washing. Bergey 
observed that when the apparatus was sterilized by steam, 
the character of the organisms present in the milk after 
it had come in contact with the milk pail, strainer, cooler, 
etc., did not differ from those found in samples taken 
directly from the udder. Milk bottles should be steril- 
ized before refilling for the additional reason that it is 
a protection against the infection of the milk supply by 
bottles which may be returned from houses where infec- 
tious disease exists. 

Exposure to live steam is the most certain method 
of destroying bacteria in milk vessels and utensils. To 
obtain complete sterilization, it is necessary to expose 
the vessels and apparatus to steam under 5 pounds pres- 
sure for 20 minutes. This is possible with the cast-iron 
sterihzers which can be tightly closed. Bottles will stand 
this amount of pressure. The galvanlzed-iron steam 
chests frequently used in dairies are not sufficiently tight 
to hold the steam under pressure ; in these, 99.2 per cent, 
of the bacteria are destroyed, the spore formers surviv- 
ing. Rinsing or scalding the vessels and utensils with 
boiling water after washing does not destroy many bac- 
teria, and while exposure to the sun has a germicidal 



DAIRY INSPECTION 191 

effect it also usually exposes the apparatus to contami- 
nation with germ-laden dust. 

When facilities for sterilization by steam are not 
available, the milk vessels and utensils may be sterilized 
by submerging them for 20 minutes in a 0.1 per cent, 
solution of hypochlorous acid after they have been 
cleansed in the usual way. Hypochlorous acid is even 
more effective as a germicide than the hypochlorites, al- 
though the latter are 150 to 200 times as powerful as 
carbolic acid. A 0.1 per cent, solution will kill typhoid 
bacilli in 2V2 minutes. The solution may be conveni- 
ently prepared as follows: Mix together equal parts by 
weight of finely ground commercial bleaching powder 
(chloride of lime) and powdered boric acid; keep in a 
well-stoppered bottle and protect from light. Dissolve 
6 drams of the powder in a quart of water by shaking 
thoroughly, let stand for 24 hours and pour off the 
clear fluid; then add 4 quarts of water. This makes a 
solution containing 0.1 per cent, of hypochlorous acid. 
When milk bottles are submerged in this solution for 
20 minutes, drained for 10 to 20 minutes, and then filled 
with milk and capped, no odor or taste of chlorine can 
be detected in the milk. Milk can be strained through 
cheese cloth moistened with the solution without any 
effect upon the odor or taste. Tin vessels are not cor- 
roded. The powder from which the solution is pre- 
pared may be kept for some time under proper condi- 
tions, but the solution rapidly loses strength and be- 
comes ineffective in three weeks. Calcium hypochlo- 
rite has been in use for a long time as a disinfectant for 
water supplies and a solution containing 1 ounce to 125 
gallons of water is recommended for the sterilization of 
milk vessels and utensils, but it is much more expensive 



192 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

than the hypochlorous acid solution. Winslow reports 
that a 1 to 1000 solution of chloride of lime may be used 
in the same manner and with the same results as the 
hypochlorous acid and the calcium hypochlorite solu- 
tions. 

When milking machines are in use, careful inquiry 
should be made regarding the method of cleaning them. 
The apparatus should be taken apart each time after 
it is used and thoroughly cleansed and sterilized. On 
account of the labor involved, this is sometimes done 
only once a day, but this is not sufficient. Particular 
attention must be given to cleaning the metalHc and 
rubber tubing and teat cups. After being rinsed with 
cold water and then with hot water, these parts should 
be disinfected. The metallic tubes may be sterilized by 
steam, together with the other metallic parts of the ap- 
paratus. The 0.1 per cent, solution of hypochlorous 
acid and the 1 to 1000 solution of chloride of lime are 
very satisfactorj^ disinfectants for the rubber tubing and 
teat cups and for the metallic parts as well. The rubber 
parts should be kept submerged in one of these solutions 
when not in use. A solution of i/4 pound of chloride 
of lime and 10 pounds of sodium chloride in 10 gallons 
of water is also recommended. If air is allowed to re- 
main in any part of the tubing, bacteria may multiply. 
The apparatus must be properly cared for or the milk 
will contain a larger number of bacteria than when it 
is drawn by hand. A milking machine is not in itself 
a protection against dirt or bacteria in milk. The hair 
on the udder around the teats must be kept short and 
this part of the udder must also be cleaned before each 
milking to obtain good results, while the teat cups must 



DAIRY INSPECTION 193 

not be permitted to fall on the floor or into the bedding 
when they become detached from the teats. 

4. Water Supply. — It is not only important that 
the water used on a dairy farm for washing the milk 
utensils and vessels shall be free from fecal contamina- 
tion, but also that the surroundings of the source of 
supply are such that there is no probability of contami- 
nation. While the first point can be decided by a bac- 
teriological examination of a sample of the water, the 
second can only be determined by an inspection of the 
water supply and its surroundings. Frequently inspec- 
tion will furnish all the information required to condemn 
a polluted water supply, but in many instances a bac- 
teriological examination will be necessary. The exami- 
nations reported of farm water supplies indicate that 
they are frequently contaminated. 

On many farms the water supply is obtained from 
springs or from dug wells. In either case, the source 
of supply is the underground water. A well is an arti- 
ficial opening from the surface down to the underground 
water, while a spring is a place where the underground 
water has come to the surface. The underground water 
is contained in the interstices between rocks, gravel, sand, 
clay, etc., at various depths below the surface of the 
ground. The level of the underground water, i.e., the 
water table, conforms in a general way to the level of 
the ground surface ( Fig. 22 ) . 

The purity of spring water depends very largely 
upon the location of the spring. When springs on farms 
are contaminated, it is usually due to pollution by sur- 
face wash or subsurface drainage. A diy closet situated 
on the slope of a hill above a spring is especially dan- 
gerous. The location of manure piles, houses, barns, pig 
13 



194 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

pens, or other structures above springs is objectionable. 
Water from springs exposed to surface drainage should 
not be used for washing dairy utensils and vessels, but 
if no other source is available the spring should be pro- 
tected by impervious walls. Open springs are sometimes 
polluted by live stock or contaminated by dust, leaves, 
and other refuse blowing into them. Pollution of springs 
by subsurface drainage is not very common on farms, 
but may occur where the layer of earth above the water 
table is thin or readily permeable. The permeability will 
depend upon the material present. Fine sand is a good 



Fia. 22. — Section showing relation of water table to surface irregularities. (From Water 
Supply Paper 255, U. S. Geological Survey.) 

filter, but coarse sand and gravel permit the water to 
pass through rapidly, carrying some of the contaminat- 
ing material through with it. Clay and till (largely clay 
and sand) are good filters. When the layer of earth 
above the water table is thin or permeable, the water in 
the spring is likely to be warm. Cesspools, buildings, 
or anything else which may be a source of pollution 
should not be placed at a higher level than a spring be- 
cause of the danger of contamination by subsurface 
drainage (Fig. 23). When cracks or fissures extend 
from the surface into the water-bearing strata, as occurs 
in rock formation, or where tubular channels have been 
formed, the spring may be contaminated. This may 



DAIRY INSPECTION 195 

occur especially in limestone districts, in which basins or 
sinks may be found on the surface which are connected 
with underground water channels. Muddy water or 
floating material in the spring after severe rains are 
indications of the existence of these conditions. 

The safety of well water depends upon the purity of 
the water at its source, which is the underground water^ 
and the protection provided against the entrance into the 
well of contaminated water or polluting material. The 
purity of the underground water in the case of a well 
will depend upon the same conditions as control the 
purity of springs. Contaminated water or polluting 



Cesspool 




Fio. 23. — How springs may be polluted by subsurface drainage. (From Water Supply 
Paper 255, U. S. Geological Survey.) 

material may enter the well through openings in the 
curbing or casing and, in open wells, from the surface 
also. 

The open or dug well is the type most commonly 
found on farms because it is the most cheaply made and 
the work can be done by ordinary farm labor. With 
certain precautions, the dug well yields a satisfactory 
supply of water, but as commonly constructed it is the 
most dangerous of all sources of water supply. A dug 
well may be contaminated by material seeping through 
the ground and curbing, or entering from the top. 
Stone, brick, or wood curbing usually contains crevices 
which permit the passage of polluting material. Such 



196 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

material may also enter through leaks or holes in the iron 
casing of drilled wells. Cesspools and privies are the 
most common sources of seepage. Material thrown out 
upon the surface of the ground may also be carried down 
through the soil by rain and seep into the well or reach 
the underground water. The "safety distance" from 
such sources of pollution will depend upon the character 
of the soil and the quantity and concentration of the 
polluting material, but a rule that may serve as a gen- 
eral guide is the following: A well drains an inverted 
cone of land whose top surface is four times as wide as 
the depth of the well. Stone or brick curbs may be made 
impervious by covering the interior surface with cement. 
This will prevent contamination by seepage unless the 
well is shallow, in which case the polluting material may 
pass down and enter the well under the bottom of the 
curb. 

One of the most common methods of pollution of 
dug wells is the entrance of material through the top. 
Dust and surface washings from pump drippings, waste 
water, and rains are the principal sources of contami- 
nation. Small animals, such as toads, mice, rats, moles, 
and snakes, fall into open wells in seeking water in pe- 
riods of drought. A water-tight iron or cement cover, 
tightly joined to the curb, will protect the well from 
these surface contaminations. 

Deep wells, driven or bored, are less likely to be pol- 
luted than dug wells or shallow bored wells because the 
underground water is protected from seepage by a much 
thicker stratum of earth and the well is protected by an 
iron casing. If cracks or leaks occur in the casing, pol- 
luting material may enter. While deep wells are subject 
to contamination, they are a much safer source of water 
supply than shallow wells. 



DAIRY INSPECTION 197 

V. SCORE CARDS 

It is important to have some system of recording 
the conditions found on inspection by which the dairy 
farm can be rated and classified according to a certain 
standard. Comparisons can then be made, when desired, 
between different dairy farms and also of the condition 
of the same farm at diiferent times. In addition, the 
rating or classification, together with the details of the 
record, will serve as a basis for an opinion as to the qual- 
ity of milk which may be expected from each farm. These 
ratings, or scores, if published, will also serve as a guide 
to the consumer in purchasing milk. 

The most satisfactory system of this kind is what is 
known as the score-card method. In this method, 100 
is taken as a perfect score and various portions of this 
nimiber are assigned to different parts of the equip- 
ment and methods, according to what is considered to 
be the relative importance of each. Each part of the 
equipment and the various methods are rated or scored 
by the inspector according to the degree with which they 
meet the standard of perfection, and the total of these 
figures constitutes the score for the dairy farm. Sev- 
eral kinds of score cards are in use. There is one pre- 
pared by Dr. W. C. Woodward, health officer of the 
District of Columbia, the originator of the score-card 
system. A score card prepared by Prof. Raymond 
Pearson, known as the Cornell score card, and another 
published by the U. S. Bureau of Animal Industry are 
also in rather general use. These three score cards are 
printed on the following pages : 



198 PRINCIPLES AND PRACTICE 01" MILK HYGIENE 



(Front of Card) 
Health Department of the District of Columbia 



SCORE CARD FOR DAIRY FARMS 

Farm of Location 

Application 

Permit 
Date 



Number Consignee. 



This score card shows conditions only at the time of this inspection. To learn of conditions gen- 
erally prevailing, reference should be made to a series of consecutive score cards. This may be done 
at the Health Office. 



A. STABLE AND TABD 

1. Stable: Site, well drained, and 

free from contaminating sur- 
roundings 

2. Construction of stable: 

Tight, sound floor and proper 
gutter, tie and manger. . ... . . 

Smooth, tight walls and ceiling 

3. Light: Four sq. ft. or more of 

glass per cow, and adequate 
artificial lighting for milking. . 
(Three sq, ft., 2; two sq. ft., 1.) 

4. Ventilation: Automatic system . 

(Adjustable windows, 1.) 
Cubic feet of air space per cow, 

1,000 to 600 

(500 to 600, 1.) 

Stable air 



B. Cleanliness: 

Floor 

Walls 

Ceiling and ledges. . . . . . 

Mangers and partitions . 

Windows 

Bedding 



6. Water for cattle: Clean and fresh 

7. Yard: Free from manure, dean 

and well drained 

(Manure stored less than 50 
feet from stable, 0.) 

8. Privy: 

(To include accommodations 
for employees.) 

Location 

Construction 

Cleanliness 

Disposal of Contents 



Total carried forward. 



Score 


Per- 
fect 


AI- 
lowed 


I 




3 

2 




3 




2 




2 




2 




2 
1 
1 
1 

I 
2 




1 




2 




1 

1 
1 
1 




30 







Total brought forward 

B. MILK HOU8E 

Site: Free from contanainating 
surroundings, with separate 


Score 




Per- 
fect 


Al- 
lowed 


1. 


30 

1 

1 

1 
1 

3 

10 
10 

10 

1 

1 

2 

6 

2 
3 

1 

2 
4 
5 

3 
3 











3. 


Construction of floor, walls, and 




4. 
5. 

1 


Light, ventilation, and screens . . 
ClearJiness of milk room, in- 
cluding freedom from flies 

C. UTENSILS 




2. 
3. 


(Removable top, 5.) 

Facilities for sterilization 

(Steam, 10; boihng water, 5.) 
Thorough cleansing and steriliz- 




4 






5. 


Construction: 

Sound, of good type, and in 




6. 

1. 

2. 


Water for cleaning, clean, con- 
venient, and sufiicient 

D. MILKING AND MILK 

Udders washed and dried • 

(Cleansed with moist cloth, 2.' 
Attendants: Cleanliness and ap- 




"i 






S 






4. 

5 


Milk of each cow removed im- 
mediately from stable 




6. 

7 


Efficient cooling ; below 50° F . . . 
(51° F. to 55° F., 2; 56° F. to 
60° F., 1.) 
Storage; below 50° F 




8 








(Jacket or wet blanket, 2; dry 
blanket or covered wagon, 1.) 

Total 






100 











Remarks. 



Source of water supply General condition of farm. 

Violation of regulations, Sec of Milk Act, Sec 

Notices served, to correct, to show cause by 



Inspector. 



DAIRY INSPECTION 



199 



(Back of Card) 
Health Department of the District of Columbia 

SCORE FOR cattle 



Number of cattle in 
dairy herd 



Perfect score. 

For each cow 

or bull, 100 



Total possible score for herd . 



Deductions on account of cattle diseased, etc. 



Number of 
Cattle 



Nature of disease, defect, etc. 



1. Tuberculosis as shown by a physical 

examination, or by the tuberculin 
test 

2. Absence of a tuberculin test within 

one year of the date of inspection, 
not to include cattle scored under 
paragraph 1 

3. Inflammatory diseases of the udder. . 

4. Diseases other th'an or in addition to 

the diseases mentioned above 

5. Unclean condition of the teats and 

udders 

6. Unclean condition of the cows other 

than specified in the preceding par- 
agraph 

7. Undue emaciation or cows otherwise 

out of condition 



Deductions 
per cow 



100 

30 
100 or less 

100 or less 

40 or less 

30 or less 
10 or less 



Total 
Deductions 



Total deductions for herd 

Net score 

Net score ( ) divided by the total possible score 

for herd ( ) equals Percentage score 

Remarks 

Inspector. 

The Health Department believes that if a cow is suffering from tuberculosis, 
her entire value as a dairy cow is gone. If she is suffering from an inflammatory 
disease of the udder as well as from tuberculosis, she becomes even a greater danger 
to the herd. And if she is furthermore otherwise diseased, or out of condition, or 
dirty, she becomes even a more serious menace to public health. For these reasons, 
the above system of scoring has been arranged so that an individual cow may 
count against the score of the entire herd more than would have been allotted to 
her had she been in perfect condition. 

All cows stabled with the dairy herd or found in the milking line will be scored 
as part of the herd. 



200 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

(Front of Card) 

tTNITED STATE3 DEPARTMiaSfT OF AGRICULTURE, BUREAU OF ANIMAL INDUSTRY 

DAIRY DIVISION 



Sanitary Inspection of Dairy Farms 



SCORE CARD 

Owner or lessee of farm. , 

P. O. address State 

Total number of cows Number milking 

Gallons of milk produced daily 

Product is sold by producer in families, hotels, restaurants, stores, to 

dealer. 

For milk supply of 

Permit No Date of inspection 191 

Remarks: 



(Signed) 

Inspector. 



DAIRY INSPECTION 

(Back of Card) 



201 



Equipment 



cows 

Health 

Apparently in good health ■_.■;• 1 
If tested with tuberculin within 
a year and no tuberculosis is 
found, or if tested within six 
months and all reacting ani- 
mals removed 5 

(If tested within a year and re- 
acting animals are found and re- 
moved, 3.) 

Food (clean and wholesome) 

Water (clean and fresh) 



Location of s table 

Well drained 1 

Free from contaminating sur- 
roundings 1 

Construction of stable 

Tight, sound floor and proper 

gutter .2 

Smooth, tight walls and ceilings 1 

Proper staD, tie, and manger. . .1 

Provision for light: Four sq. ft. of 

glass per cow 

(Three sq. ft., S; 2 sq. ft., 2; 1 sq. 
ft., 1. Deduct for uneven distri- 
bntion.) 

Bedding 

Ventilation 

Provision for fresh air, control- 
able flue system 3 

(Windows hinged at bottom, 
1.5; sliding windows, 1; 
other openings, 0.5.) 
Cubic feet of space per cow, 600 

ft 3 

(Less than 500 ft., 2; less than 

400 ft., 1; less than 300 f t.,0.) 
Provision for controlling tem- 
perature 1 



Construction and condition of uten 
sils 

Water for cleaning 

(Clean, convenient, and abundant.) 

Small-top milking pail 

Milk cooler 

Clean milking suits 



MILK ROOM OB MILK HOUSE 

Location; Free from contaminating 
surroundings 

Construction of milk room 

Floor, walls, and ceilings 1 

Light, ventilation, screens .... 1 

Separate rooms for washing utensils 
and handling milk 

Facilities for steam 

(Hot water, 0.5.) 



Score 



Per- Al- 
fect lowed 



Total 40 



Methods 



Score 



cows 

Clean 

(Free from visible dirt, 6.) 



Cleanliness of stables 

Floor 2 

Walls 1 

Ceilings and ledges 1 

Mangers and partitions 1 

Windows •.••••: ^ 

Stable air at milking time 

Freedom from dust 3 

Freedom from odors 2 

Cleanliness of bedding 

Barnyard 

Clean 1 

Well drained 1 

Removal of manure daily to 50 feet 
from stable 



MILK ROOM OB MILK HOCBE 

Cleanliness of milk room 



UTENSILS AND MILKING 

Care and cleanliness of utensils 

Thoroughly washed . 2 

Sterilized in steam for 16 min- 
utes 3 

(Placed over steam jet, or scalded 

with boiling water, 2.) _ 

Protected from contamination. .3 

Cleanliness of milking 

Clean, dry hands 3 

Udders washed and wiped.... 6 
(Udders cleaned with moist cloth, 

4; cleaned with dry cloth or brush 

at least 15 minutes before milking, 

1.) 

HANDLING THE MILK 

Cleanliness of attendants in milk 



room 

Milk removed immediately from 

stable without pouring from pail . . 
Cooled immediately after milking 

each cow 

Cooled below 50° F 

(51° to 55°, 4; 56° to 60°, 2.) 
Stored below 50° F 

(51° to 55°, 2; 66° to 60°, 1.) 
Transportation below 60° F 

(51° to 55°, 1.5; 56° to 60°, 1.) 

(If delivered twice a day, allow 
perfect score for storage and trans- 
portation.) 



Total. 



Per- Al- 
fect lowed 



60 



Equipment -{-Methods = Final Score. 

Note 1. — If any exceptionally filthy condition is fo\ind, particularly dirty utensils, the total score 
may be further limited. 

Note 2. — If the water is exposed to dangerous contamination, or there is evidence of the presence 
of a dangerous disease in animals or attendants, the score shall be 0. 



202 



PRINCIPLES AND PRACTICE OF MILK HYGIENE 



Department of Dairy Industry, College of Agriculture, 
Cornell University 



SCORE CARD FOR PRODUCTION OF SANITARY MILK 



Date. 



Dairy of. 





Health and comfort of the cows and their isola- 
tion when sick or at calving time 


Per- 
fect 


Score 


I. Health of the 


45 
35 
20 




protection 


Location, lighting and ventilation of the stable . 
Food and water 






Total 






100 












Cows 


30 
20 
20 
30 






Stable 






Barnyard and pasture 




roundings 


Stable air (freedom from dust and odors) 

Total 






100 










lU. Construction 


Construction of utensils and their cleaning and 
sterilizing 


40 

25 
20 
15 




the utensils 


Water supply for cleaning and location and pro- 
tection of its source 






Care of utensils after cleaning 






Use of small-top milking pail 






Total 






100 










IV. Health of em- 


Health of employees 


45 
30 
25 




ployees and 
manner of 


Clean over-all milking suits and milking with 
clean, dry hands 




milking 


Quiet milking, attention to cleanliness of the 
udder and discarding fore-milk 






Total 






100 










V. Handling the 
milk 


Prompt and eflScient cooling 


35 

35 
30 




Handling milk in a sanitary room and holding it 
at a low temperature 






Protection during transportation to market .... 
Total 






100 












Total of All Scores 


500 











If the total of all scores is 

480 or above 

450 or above 

400 or above 

Below 400 



And each division is The sanitary conditions are 

... 90 or above Excellent 

... 80 or above Good 

... 60 or above Medium 

... Or any division is below 60 Poor 



The sanitary 

conditions are . 



Scored by. 



CHAPTER VIII 

PASTEURIZATION 

Pasteurization of milk consists in heating the milk 
at various temperatures below boiling for a variable 
period of time. The term pasteurized milk is very indefi- 
nite in its meaning because the process is not always car- 
ried out in the same manner, but since 1913, when the 
Commission on Milk Standards of the New York Milk 
Committee published its second report, there has been 
more uniformity in this country than formerly with re- 
gard to temperature and time of exposure, state and 
local authorities having very generally accepted the 
standard adopted by the Commission. This standard 
specifies 140 to 155° F. (60 to 68° C.) as the minimum 
temperature at which the milk shall be heated, the mini- 
mum period of exposure to be 20 minutes at 140° F. 
(60° C), with one minute less for each degree of tem- 
perature above 140° F. But, at the same time, in order 
to allow for the variations in temperature and holding- 
time which may occur under commercial conditions, the 
Commission recommended that the milk be heated to 
at least 145° F. (62.8° C.) for at least 30 minutes. In 
Europe, pasteurized milk is usually milk which has been 
heated for a few moments at 176° F. (80° C.) or above, 
although within recent years the method of heating the 
milk at a lower temperature for a longer period has 
been adopted to some extent. 

When the first commercial milk pasteurizer was in- 
troduced into this country in 1895, pasteurization was 
recommended to milk distributers as a means of pre- 

203 



204 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

venting milk from spoiling, and the process was adopted 
by some dealers for this purpose, being used secretly by 
many of them. Naturally, this brought the process into 
disrepute. Sanitarians and public health authorities were 
also disposed to discourage its use because of the ineffi- 
ciency of the early apparatus and the lack of exact in- 
formation regarding the effect of the process upon the 
milk and the pathogenic organisms which may be con- 
tained in it. With the acquirement of further informa- 
tion on the latter phaje of the subject and improvement 
of the apparatus, sanitarians and public health officials 
came to regard the pasteurization of milk, when prop- 
erly carried out, as a legitimate and useful process and 
by 1910 the pendulum had swung so far in the other 
direction that many of them were advocating the pas- 
teurization of all milk. 

PRINCIPLES OF PASTEURIZATION 

To obtain a correct conception of the hygienic value 
of pasteurization, it is necessary to consider the effect of 
different degrees of heat and periods of exposure upon 
the pathogenic organisms which may be present in the 
milk, upon the common milk bacteria, upon the toxins 
and decomposition products resulting from bacterial 
growth, upon the nutritive properties of the milk, and 
upon the ferments or enzymes. Commercially, the effect 
upon the taste and the separation of the cream is also 
of importance. 

1. Effect of Heat on Pathogenic Organisms. — The 
disease-producing bacteria which occur most frequently 
in milk are streptococci, the bacilli of tuberculosis, ty- 
phoid fever and diphtheria, and the pyogenic staphylo- 
cocci. The infectious agent of scarlet fever, which is 



PASTEURIZATION 205 

also sometimes transmitted by milk, has not been iden- 
tified. Of the organisms mentioned, the tubercle bacillus 
is the most resistant to heat, with the possible exception 
of some varieties of streptococci. The streptococci of 
septic sore throat are destroyed by heating at 140° F. 
(60° C.) for 30 minutes (Davis) or at 145° F. (62.8° 
C.) for 20 minutes (Hamburger), and exposure to a 
temperature of 125.6 to 143.6° F. (52 to 62° C.) for 
30 minutes is sufficient to kill Streptococcus pyogenes 
( Kitchens ) . There are some varieties of streptococci 
which are more resistant to heat, but we have no reason 
to believe that those which occur in milk are pathogenic. 
It seems very probable that heating milk sufficiently to 
destroy tubercle bacilli will also kill any pathogenic strep- 
tococci which may be present. A temperature of 140° F. 
(60° C.) for 2 minutes will destroy the bacilli of typhoid 
fever and diphtheria. The question of the amount of 
heat required to destroy the pathogenic organisms which 
occur most frequently in milk consequently resolves it- 
self into a question of how much heat is necessary to kill 
the tubercle bacillus. The evidence on this point must 
therefore be considered. 

Bang found that heating milk momentarily at 185° 
F. (85° C.) destroyed tubercle bacilli in naturally in- 
fected milk, and Jensen reports experiments in which 
tubercle bacilli in milk were killed by a few moments 
exposure to 158 to 176° F. (70 to 80° C.) . On the other 
hand. Grimmer and other investigators are of the opinion 
that, when the exposure is momentary, a temperature of 
at least 194° F. (90° C.) is necessary to insure the de- 
struction of the bacilli in all cases. 

Concerning the effects of a more prolonged exposure 
at lower temperatures, experimental results are even 



206 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

more divergent. Woodhead reports that while in some 
experiments a temperature of 140° F. (60° C.) killed 
tubercle bacilli in 25 minutes, in others an exposure of 
8 hom-s was required. Yersin, Bitter, Bonlioff, and other 
investigators report that although an exposure to 140° 
F. (60° C.) for one hour was nearly always fatal to 
tubercle bacilli, the effect was uncertain when the time 
of exposure was much shorter. In Foster and Rull- 
mann's experiments, the bacilli remained alive after 45 
minutes at 140° F. (60° C). DeJong asserts that tu- 
bercle bacilli will survive heating at 159.8 to 161.6° F. 
(71 to 72° C.) for % hour, while Van der Sluis de- 
clares that a temperature of 176° F. (80° C.) for 1 hour 
is necessary to kill tubercle bacilli in naturally infected 
milk. Hittcher considers 1 hour at 140 to 145.4° F. (60 
to 63° C), 45 minutes at 147.2 to 149° F. (64 to 65^ C), 
or 30 minutes at 150.8 to 158° F. {66 to 70° C.) neces- 
sary to destroy tubercle bacilli. On the other hand, Hew- 
lett, in England, found that tubercle bacilli did not sur- 
vive 30 minutes exposure to 140° F. (60° C.) and, in 
this country, Rosenau found 20 minutes at 140° F., 
Theobald Smith 15 minutes at 140° F., and Russell and 
Hastings 10 minutes at that temperature sufficient to 
kill the organisms. Hewlett and the American investi- 
gators used in their experiments milk artificially in- 
fected with tubercle bacilli, while nearly all, if not all, 
of the other experiments mentioned were made with 
naturally infected milk. 

The conditions were therefore by no means the same. 
In naturally infected milk, the tubercle bacilli are em- 
bedded in masses of mucus, clots of fibrin, or shreds of 
tissue, and this albuminous covering protects them from 
the action of the heat. It is true that in those experi- 



PASTEURIZATION 207 

ments in which milk from tuberculous udders was used 
without being diluted with normal milk that the circum- 
stances were not the same as exist under natural condi- 
tions; the infection was much more concentrated, and 
there was not the same opportunity for the albuminous 
matter surrounding the bacilli to be softened and loos- 
ened as occurs when a small quantity of infected milk 
is mixed with a comparatively large quantity of normal 
milk several hours before pasteurization. But individual 
milk was not used in all of the experiments with natu- 
rally infected milk ; some of them were made with mixed 
milk which was entirely normal in appearance. 

In all of the experiments referred to a small quantity 
of milk was heated in a laboratory. Under these condi- 
tions, the temperature at which the milk is heated and 
the time of exposure can be accurately controlled. But 
in commercial pasteurizers fluctuations in temperature 
and variations in holding- time cannot be entirely avoided 
and when large quantities of milk are pasteurized under 
these conditions there is not the same assurance that every 
particle of milk will be heated at the same temperature 
for the same length of time as when a small quantity of 
milk is heated in the laboratory. This is shown by the 
experiments of Rosenau and Schorer in which they tested 
the efficiency of pasteurization under commercial condi- 
tions. They inoculated milk with cultures of the bacilli 
of typhoid fever, diphtheria, and tuberculosis and en- 
deavored to heat it at 140 to 145° F. (60 to 62.8° C.) 
for different periods of time. Two tests were made with 
typhoid bacilli and in one the organisms survived. The 
same results were obtained with the diphtheria bacillus. 
In two tests with tubercle bacilli of the bovine type one 
failed, and in a similar experiment with tubercle bacilli 



208 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

of the human type the organisms were not killed in either 
test. As a result of these experiments, Rosenau and 
Schorer concluded that in order to allow a margin of 
safety when milk is pasteurized under commercial condi- 
tions it is necessary to expose the milk to a temperature 
of at least 145° F. (62.8° C.) for 30 to 45 minutes. 

The only experiment recorded in which naturally 
infected milk was pasteurized in large quantity under 
commercial conditions was made by Tramn and Hart, 
who published their results in 1916. The milk came 
from a large herd of reacting cows and the volume 
amounted to from 700 to 1000 quarts daily. Samples 
were taken at the milk station in the city before and after 
pasteurization. Twenty-four samples of raw milk were 
tested on guinea pigs and all except one sample produced 
tuberculosis in the test animals, and the guinea pigs inoc- 
ulated with this sample died of septicemia before there 
was an opportunity for tuberculosis to develop. Eleven 
samples of milk which had been heated at 140° F. (60° 
C.) for 20 minutes were tested in the same manner and 
did not produce tuberculosis in a single instance. Twelve 
samples of milk which had been heated above 140° F. 
(60° C.) for a longer period than 20 minutes also proved 
free from tuberculosis infection. While these results ap- 
pear to indicate that 140° F. (60° C.) for 20 minutes 
will kill tubercle bacilli in naturally infected milk when 
it is pasteurized under commercial conditions, it would 
seem desirable, in view of the contradictory data fur- 
nished by the other experiments which have been men- 
tioned, to have them confii-med by further tests before 
drawing final conclusions. There ought to be absolute 
certainty that a given temperature and period of expo- 
sure will kill tubercle bacilli and other pathogenic organ- 



PASTEURIZATION 209 

isms in natui*ally infected milk before they are adopted 
as a standard for pasteurized milk. 

2. JE'ffect of Heat on the Common Milk Bacteria. — 
The effect of pasteurization upon the common milk bac- 
teria is of importance because if, for example, the lactic 
acid bacteria are destroyed and peptonizing or gas-form- 
ing organisms survive the milk may undergo putrefac- 
tion instead of souring. Moreover, the putrefactive 
changes may advance sufficiently to render the milk in- 
jurious before the appearance or taste is altered. 

The action of different degrees of heat upon the com- 
mon milk bacteria has been very thoroughly studied by 
Ayers and Johnson. In their experiments, when milk 
was heated to 170° F. (76.7° C.) or above, the majority 
of the organisms surviving were peptonizers, but when 
the temperature was kept below 170° F. the acid-formers 
predominated among the surviving organisms. Acid 
was formed slowly, however, when the temperature had 
reached 160° F. (71.1° C). The character of the 
changes which the milk will undergo after pasteuriza- 
tion will depend not only upon the kind of bacteria which 
predominate after heating, but also upon the tempera- 
ture at which the milk is kept. If pasteurized milk is 
not cooled promptly and kept cool it undergoes putre- 
faction, especially if it has been exposed to high degrees 
of heat. Milk heated at a low temperature, 145° F. 
(62.8° C.) for 30 minutes, when kept at 50 °F. (10° C), 
will curdle and sour like raw milk, but much more slowly. 
If milk treated in this manner is stored too long, it may 
develop a strong, old taste as a result of the growth of 
the alkali-forming bacteria which survive this amount 
of heat. 

Pasteurization destroys or weakens the germicidal 

14 



210 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

power of milk. It was therefore naturally supposed that 
bacteria would develop more rapidly in pasteurized than 
in raw milk. Rickards compared the average increase 
of bacteria occurring in a number of samples of raw and 
pasteurized milk and f oimd that bacteria multiplied four 
times faster in commercially pasteurized milk than in 
raw milk at ice-box temperature. Ayers and Johnson 
contend, however, that when the growth of bacteria in 
pasteurized milk is compared with the growth of bacteria 
in the same grade of raw milk the increase of bacteria 
is about the same in both kinds of milk. But Savage 
is of the opinion that organisms which gain access to 
milk after pasteurization will grow more rapidly than in 
raw milk if for no other reason than because the bac- 
terial content is much less and the conditions for growth 
therefore much more favorable. These facts illustrate 
the importance of promptly cooling pasteurized milk and 
keeping it cool, and also indicate the necessity of pre- 
venting the access of any bacteria, and especially patho- 
genic organisms, after pasteurization. 

3. Toxins and Decomposition Products. — The 
growth of bacteria in milk is attended by the produc- 
tion of toxins and also by the decomposition of some of 
the milk constituents. The extent to which these changes 
occur will depend upon the number of bacteria which 
gain access to the milk during the drawing of the milk 
and its subsequent handling, the age of the milk at the 
time of pasteurization, and the temperature at which it 
has been kept in the meantime. 

While the true or soluble toxins (exogenous, extra- 
cellular) are destroyed at comparatively low tempera- 
tures, the endotoxins (endogenous, intracellular) are 
quite resistant to heat. Most of them require a tempera- 



PASTEURIZATION 211 

ture of 70° C. (158° F.) for their destruction, and some 
will even survive boiling. Therefore, there is no cer- 
tainty that all toxins which may be present in milk will 
be destroyed even if the milk is boiled. While there 
is no direct proof that milk containing toxins is injurious 
to health, at the same time we are also without positive 
knowledge that such milk is harmless ( see page 45 ) . 

Although there is no definite information regarding 
the effect of heat upon the cleavage products resulting 
from the breaking up of the milk constituents by bac- 
teria, we have reason to believe that they are not all 
destroyed by heat. This is an important point because 
some of these substances are of a harmful character. 

In the light of our present knowledge regarding the 
effects of pasteurization upon toxins and cleavage prod- 
ucts, it would seem advisable to limit the production of 
these substances as much as possible by protecting the 
milk from bacterial contamination and by promptly 
cooling it and keeping it cool until it is pasteurized. There 
should be a limit to the number of bacteria which may 
be present in milk which is to be pasteurized, and this 
limit should be as low as circumstances will permit. 

4. Nutritive Properties. — The statement is fre- 
quently made that milk may be heated at 145° F. (62.8° 
C.) for thirty minutes without affecting its nutritive 
properties, but this is not confirmed by the experience 
of Hess, who saw scurvy develop in from two to three 
months in nearly every one of a group of infants who 
were being fed on milk pasteurized in that manner ; when 
orange juice or potato water was added to the milk the 
disease was cured. The observations of Plantenga indi- 
cate that this diseased condition is not due entirely to 
the effect of heat on the milk. He reports that while 



212 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

scurvy developed in 23 per cent, of the children fed on 
milk which was pasteurized 24 hours after it was drawn 
from the cow by heating it at 158° F. (70° C.) for 30 
minutes, not a single case of the disease appeared in chil- 
dren receiving milk pasteurized immediately after being 
drawn from the cow, although it was from the same dairy 
and was pasteurized in the same manner. While many 
instances have been reported in which infants have been 
fed on pasteurized milk without harm, there appears to 
be no reason to doubt that milk loses some of its antiscor- 
butic properties in the process of pastem-ization and that 
the age of the milk is also a factor in bringing about the 
change. 

The opinion prevails among medical practitioners 
that pasteurized or boiled milk is the cause of rickets 
and malnutrition, as well as scurvy, in children. The 
development of rickets under such circumstances has 
been attributed to the conversion of the soluble phos- 
phates of lime and magnesia contained in milk into an 
insoluble form by the action of the heat. Malnutrition 
is thought to result from pasteurized or boiled milk being 
less digestible than raw milk, a condition which is be- 
lieved to be due to the heat coagulating the proteids and 
rendering them less susceptible to the action of the diges- 
tive fluids. According to Rupp, however, heating milk 
at 145° F. (62.8° C.) for 30 minutes does not affect 
the soluble phosphates or the albumin. The coagulation 
of the albumin begins at 150° F. (65.6° C.) and increases 
with the temperature, but the soluble phosphates are not 
affected by temperatures up to 155° F. (68.3° C). 
Feeding experiments with animals to determine the com- 
parative digestibility of raw and boiled milk have given 
contradictory results. While in most instances no dif- 



PASTEURIZATION 213 

ferences were observed, in some cases calves fed on boiled 
milk developed a diarrhoea which disappeared when raw 
milk was substituted. 

5. Ferments or Enzymes. — In the opinion of some 
authorities, the ferments or enzymes contained in milk 
play a very important role in its digestion and assimila- 
tion. From this standpoint the effect of heat on these 
substances is therefore an important consideration in 
connection with the pasteurization of milk. Most of the 
ferments in milk can withstand a temperature of from 
60 to ^5" C. (140 to 149° F.) for some time, while higher 
temperatures weaken or destroy them. 

6. Taste. — Milk does not acquire a cooked taste un- 
less it is heated to 158° F. (70° C.) or above. 

7. Cream Line. — If milk is exposed to a temperature 
of 70° C. (158° F.) or above, the cream will not sepa- 
rate. A temperature of Q5° C. (149° F.) for 10 min- 
utes has no effect on the separation of the cream, but 
as the time of exposure to this temperature is increased 
beyond this period the separation of the cream is de- 
layed more and more until finally, after 40 minutes ex- 
posure, it does not separate at all. A temperature of 
145° F. (62.8° C.) for 30 minutes and 60° C. (140° F.) 
for as long as 50 minutes has no effect on the formation 
of the cream layer. In the commercial pasteurization 
of milk, the pimiping and stirring necessary to force 
the milk through the heater and to bring it in contact 
with the heated surfaces may have the effect of breaking 
up the fat globules and thus interfere with cream sepa- 
rating even when the temperature has not been suffi- 
ciently high to alone affect the cream line. 

Summarizing the facts which have been definitely 
established regarding the effects of pasteurization, we 



214 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

find that a temperature of 145° F. (62.8° C.) for 30 to 
45 minutes, under commercial conditions, will destroy 
the pathogenic bacteria which are most likely to occur 
in milk, with the possible exception of tubercle bacilli, 
and it appears probable that this organism will also be 
destroyed, although it would be desirable to have more 
definite information on this point. Exposure to heat 
to this extent, however, cannot be depended upon to 
destroy all of the toxins and the decomposition products 
which may be present in milk as a result of bacterial 
gi'owth, while, at the same time, it destroys the antiscor- 
butic properties of milk. Moreover, it is not certain 
that it does not decrease the digestibility of milk. 

METHODS OF PASTEURIZATION 

There are three methods of pasteurization: 

1. The "flasJi' or continuous process, in which the 
milk flows continuously and is exposed to a heated sur- 
face for a few seconds. 

2. The "holder" process, in which the milk is heated 
to a certain temperature and is then held at that tem- 
perature for a certain period. 

3. Pasteurization in the Final Container. — In this 
method, the raw milk is placed in the bottle in which it 
is to be delivered, the bottle is capped, and the filled 
bottle is then exposed to the desired degree of heat. 

The "flash" process is less reliable than the "holder" 
method, as not all of the milk is certain to be heated to 
the temperature registered by the thermometer; some 
may be heated in excess of the temperature intended and 
thus balance any deficiency of temperature in the milk 
which may not be heated to the desired temperature. 
Furthermore, a higher degree of heat is required to de- 



PASTEURIZATION 215 

stroy pathogenic organisms by the "flash" method than 
by the "holder" method. Pasteurization in the final con- 
tainer is the best method, because it does not afford any 
opportunity for the milk to be reinfected. But most 
of the apparatus constructed to pasteurize milk in bot- 
tles is rather costly and it is also more expensive to oper- 
ate than that of the " flash " or " holder " variety. Fm*- 
thermore, the bottles must be tightly sealed, and this 
requires the use of a cap which is more expensive than 
the ordinary kind. Space must be allowed for the ex- 
pansion of the milk when it is heated, consequently the 
bottles cannot be entirely filled. Larger bottles must 
therefore be provided or the consumer will receive short 
measure. The vacant space permits the milk to be 
shaken about, which may disturb the cream. The cream 
may also "butter" if the milk is subjected to sufiicient 
agitation while warm. 

The milk should be cooled immediately after pasteur- 
ization. Sudden cooling following exposure to heat 
has no effect in destroying bacteria, as was formerly sup- 
posed, but prompt cooling will retard the development 
of the bacteria or spores which survive pasteurization. 
The regulations of the Philadelphia Board of Health 
requu-e that the milk shall be cooled to 50° F. (10° C.) 
or below immediately after pasteurization, held at that 
temperature or below while at the pasteurizing plant, 
and delivered to the consumer within 24 hours. The 
requirements of the New York Commission on Milk 
Standards specify that the milk must be cooled imme- 
diately to a temperature not exceeding 50° F. (10° C.) 
and held at that temperature until delivered to the con- 
sumer. 

Types of Pasteurizers. — Various types of pasteuriz- 



216 



PRINCIPLES AND PRACTICE OF MILK HYGIENE 



ing apparatus are in use. In all of those used in the 
"flash" and "holder" method, the milk is exposed in some 
way to surfaces heated by hot water or steam. Hot 



oirriET 



THERMOMETER 



Af/U{ 
WL£T 




STEAM 
/A/LET 



STEAM AND 
— WATER 
JACKET 



REVOLWA/G 
PADDLE 



Cf/AMBEI? 



Fia. 24. — A pasteurizer of simple type (B. A. I. Giro. 184). 

water is best; it maintains the heating surfaces at a 
more even temperature and the milk is less likely to be 
scorched than when steam is used. To meet the neces- 
sary requirements, a pasteurizer must heat all of the 



PASTEURIZATION 



217 



milk to the desired temperature; it must be reliable in 
operation, and must be convenient to clean. If a film is 
permitted to form on the top of the milk, which will 
occur when milk is heated in open vessels, more heat 
will be required to destroy the bacteria contained in the 
film than in the other parts of the milk. 



,HOT WAT£R HOT WATER. 

OUTLET \ /A/LET 



M/LK^ 
/A/LET 




EA/D V/EW 
(Pipe connecHone removed 
/v ^how doub/e fubes. 



WAT£R 



M/LH" 



^ 



S/DE l/JEW 



FiQ. 25.— (B. A. I. Circ. 184). 

A pasteurizer of simple style is shown in Fig. 24. 
The milk enters through the milk inlet at the bottom 
and is forced against the heated sides by the revolving 
paddle. Another type of pasteurizer is shown in Fig. 
25. This is a system of double tubes or pipes. The 
milk flows through the inner tube in one direction and 



218 



PRINCIPLES AND PRACTICE OF MILK HYGIENE 



the hot water through the outer tube in the opposite 
direction. The end connections are removable to facih- 
tate cleaning. Fig. 26 shows a "starter can" adapted 
to pasteurize small quantities of milk. It may also be 
used as a cooler. 







II 
II 

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II 

II 
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II 
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II 

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♦ -— ./^(TArr 



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P/IDDt£ 



tv/iT£/? sMce 






-Af/l/f 0(/rt£T 



FiQ. 26.— (B. A. I. Circ. 184). 



In the "flash" method of pasteurization the milk 
passes from the pasteurizer over a cooler. Sometimes 
a regenerative cooler is used in which the milk to be 
pasteurized flows down one side of a corrugated sheet 
of metal and the milk coming from the pasteurizer flows 
down the other side, the cold milk thus absorbing some 



PASTEURIZATION 



219 



of the heat from the hot milk before the latter reaches 
the cooler. ( See Fig. 27.) In the "holder" method, the 
milk is run from the pasteurizer or heater into the holder 
or retarder to be held at a certain temperature for a 
certain period of time. In the holder, the milk stops 




/i^srscfJ9Jizeo 



tx/TLsr /tuf coco 



FiQ. 27. — Regenerative Cooler. (B. A. I. Giro. 184). 



flowing and is actually held for the required time. On 
the other hand, in the retarder the flow continues, but is 
slowed or retarded sufficiently to hold the milk for the 
required period. The retarder is not as reliable as the 
holder. A simple and cheap holding tank is shown in 



220 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Fig. 28. It was made by dividing a receiving tank of 
100 gallons capacity into four compartments of 25 gal- 
lons capacity each and providing an outlet valve and a 
cover for each compartment. Fig. 29 shows a retarder 
of the tank type. The milk from the pasteurizer enters 
at A and is carried by the pipe to the bottom of the 
first compartment. When this is filled, it overflows into 
the trough C, whence the milk flows through a 
pipe leading to the bottom of the second compartment. 
The other compartments are filled successively in the 




"Ocrrter to cooler 

Fig. 28.— a simple holding tank (B. A. I. Circ. 184). 

same manner. When the last compartment overflows 
the milk enters the funnel B and passes to the cooler. 
After all the milk has come over from the pasteurizer, 
the tank is emptied by removing the funnel B and then 
taking out the plugs from each compartment succes- 
sively. 

A combined pasteurizer and holder, which may also 
be used to cool the milk, is shown in outline in Fig. 30. 
After the milk has been heated to the temperature de- 
sired and held for the required time, it can be cooled 
by replacing the hot water with cold water and then 
with ice water or brine. 



PASTEURIZATION 



221 



-/? 




Fig. 29. — Retarder of the tank type (B. A. I. Circ. 184). 




Fig. 30. — A combined pasteurizer and holder (B. A. I. Giro. 184). 



222 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

There should be an accurate thermometer in the out- 
flow pipe of the pasteurizer and one in the outflow pipe 
of the holder. A reliable temperature and time-record- 
ing apparatus should be connected with both thermom- 
eters and the records should be kept on file for official 
inspection. These records should show the time of hold- 
ing as well as the temperature. The efficiency of the 
pasteurizing apparatus should also be tested frequently 
by bacteriological tests. 

The commercial pasteurization of milk should be 
permitted only under careful and competent official su- 
pervision. The inefficiency of commercial pasteurization 
without proper supervision has been frequently demon- 
strated. Two of the worst milk-borne epidemics which 
have occurred within recent years (Chicago 1911, Balti- 
more 1912) were due to infected milk which was sup- 
posed to have been pasteurized. 

Biorization. — This process consists in spraying milk 
into a chamber in which it is exposed to a temperature 
of 167° F. (75° C.) while under a pressure of 3 to 4 
pounds. The apparatus, which is called a biorizator, was 
invented by Dr. Oscar Lobeck, in Germany, in 1912. 
The inventor claims that by this process all of the harm- 
ful bacteria are destroyed, while the color, odor, taste, 
albumen, ferments, salts, and cream line are not affected. 

It has been proposed to destroy bacteria in milk by 
subjecting them to the action of ultra-violet rays, elec- 
tricity,, and ozone, but the processes in which these agents 
are used have all proved less satisfactory than pasteuri- 
zation. 



CHAPTER IX 

METHODS OF EXAMINING MILK 

Milk may be subjected to various methods of exami- 
nation for the purpose of detecting adulteration or dilu- 
tion, the addition of preservatives, or the presence of 
pathological products, and for the determination of the 
reaction, the bacterial content, the relative number of 
leucocytes, the quantity of sediment or dirt, etc. 

Collecting Samples. — When milk is permitted to 
stand undisturbed, the fat rises to the top and the heavier 
substances settle to the bottom. Some of the cells and 
bacteria gravitate to the bottom, but many of them are 
carried up with the fat. The upper part of the milk 
contains more fat than the lower even before a cream 
layer is visible. For these reasons, the milk in the con- 
tainer should be thoroughly mixed before a sample is 
taken for examination. When the milk is cold, consid- 
erable shaking or stirring is required to mix the fat 
equally. In collecting samples of which the specific grav- 
ity, the per cent, of fat and total solids or the acidity 
are to be determined, or which are to be tested for pre- 
servatives, alkalies, nitrates and nitrites, etc., the same 
dipper may be used in taking the different samples with- 
out affecting the accuracy of the tests. There appears 
to be some danger, however, of carrying typhoid fever 
and diphtheria infection over from one sample to an- 
other, although we have no proof of this having actually 
occurred. The same dipper may be used for stirring 
and mixing the milk. But when the bacterial content 
or the ferment reactions are to be determined, each sam- 

223 



224 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

pie must be collected in such a manner as to avoid the 
contamination of one sample by another. The most sat- 
isfactory plan is to have a sufficient number of sterile 
pipettes or aluminum tubes of suitable size and to use 
a separate pipette or tube for each sample. ( See method 
described on page 261.) The extension of the custom 
of delivering milk in bottles has greatly simplified the 
collection of samples for laboratory examination, espe- 
cially for the bacteriological and ferment tests. 

An instrument kiiown as a "milk thief" is frequently 
used to collect samples of milk from vessels with straight 
sides, like shipping cans. It consists of a metal tube 
about 23 inches long vrith a handle at the upper end. 
This tube is inserted slowly into the can of milk in a 
perpendicular position until the lower end of the tube 
rests on the bottom of the can. The interior of the tube, 
of course, fills with milk. The opening at the top is 
closed tightly with the thumb, and the tube is then lifted 
out of the can, cariying with it the column of milk in 
the interior. The milk thus withdrawn may be emptied 
into a vessel by removing the thumb from the top of the 
tube. By this means, a column of milk extending from 
the bottom to the top of the fluid is obtained, which in- 
cludes all of the different strata existing at various levels 
in the can and which may therefore be regarded as a 
representative sample. Another type of tube sampler 
has a cap at the lower end with three openings, which 
are closed when the cap comes in contact with the bottom 
of the can. As the tube is pushed down into the can, 
the milk enters its interior through these openings and 
is held there when the cap is closed. The tube is then 
withdrawn and the milk emptied into a vessel. 

Preserving Samples. — When the samples are to be 



METHODS OF EXAMINING MILK 225 

shipped some distance to a laboratory to be tested for 
specific gravity, fat per cent., and per cent, of total solids, 
or to be subjected to any of the chemical tests, an anti- 
septic may be added to preserve them. Potassium dichro- 
mate, % gram to the liter of milk (7% grains to the 
quart) and formalin, 20 drops to the liter, are usually 
used for this purpose. It is better, however, to sterilize 
the sample bottle by boiling and to close it with a steril- 
ized stopper. This method must be followed when bac- 
teriological or ferment tests are to be made, as antiseptics 
cannot be added in such cases, and the samples should 
be packed in ice. 

Stable or Herd Samples. — When a sample of market 
milk is tested and it appears from the results that the 
milk has been diluted with water or that it has been 
skimmed or diluted with skimmed milk, a stable or herd 
sample may be taken at the dairy farm from which the 
suspected milk came and tested for comparison. On the 
day the herd sample is taken, the cows should be fed, 
watered, and milked as usual and by the regular persons ; 
the two milkings should be thoroughly mixed and the 
sample taken from the whole. If nitrates or nitrites have 
been found, samples of the water should also be taken 
and examined. The importance of the stable or herd 
test is variously regarded. Some authorities do not con- 
sider it of much value, especially for small herds, because 
of the daily variation in the composition of the milk of 
the cow, particularly in the per cent, of fat. Others do 
not believe that accepted averages of the specific gravity 
and composition of normal milk are a safe basis for judg- 
ing milk in regard to dilution or skimming, and are of 
the opinion that a definite conclusion can only be reached 

15 



226 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

after a herd sample is tested and the results compared. 
The establishment of a legal standard for the per cent, 
of fat and total solids in milk has made it unnecessary in 
many states to prove that milk has been actually diluted 
or skimmed. All that is required is to show that the 
fat and total solids are below the legal standard; con- 
sequently the question of taking a stable sample for com- 
parison does not arise. 

Individual Samples. — When a sample of milk is 
taken from an individual cow for the determination of 
the specific gravity and the per cent, of fat and total 
solids, the milk should be drawn into a pail in the usual 
manner and the sample taken from the pail after the 
milk has been thoroughly mixed. If it is desired to ascer- 
tain the average for the day, which is the usual method, 
an equal quantity of milk is taken from the morning and 
evening milking, mixed, and then tested. When the 
ferment tests are to be applied or the number of bacteria 
is to be determined, the sample must be drawn with a 
sterile pipette and placed in a sterile bottle, the contents 
of the pail being first thoroughly mixed. If the milk is 
to be examined for pathological conditions, a small quan- 
tity may be milked from each quarter into a sterile bottle ; 
it is best, however, to have each quarter milked dry and 
to collect a small quantity of milk at the beginning, in 
the middle, and at the end of the milking. 

Mixing the Milk Sample. — Previous to removing 
milk from the sample bottle for a test in the laboratory, 
the milk should be thoroughly mixed. This may be 
done by inverting the bottle several times if it is tightly 
stoppered, or by pouring the milk from the bottle into a 
beaker and back again several times. No cream should 



METHODS OF EXAMINING MILK 227 

be permitted to adhere to the stopper or to the sides of 
the bottle. If the bottle has been standing for several 
hours and the milk has been thoroughly chilled, it may 
be necessary to warm the sample in order to avoid this. 

Color, Consistency, Odor, and Taste. — As a prelim- 
inary examination, the color, consistency, odor, and taste 
of the milk should be observed. The senses of smell and 
taste soon tire, however, and it is therefore not possible 
to properly examine many samples consecutively. 

A bluish tinge may indicate a low per cent, of fat, 
skimming, or watering, but it must be remembered that 
any milk will have a bluish tinge if in a thin layer. A 
reddish tinge is sometimes observed in milk from an 
udder affected with mastitis. Various other changes in 
color may occur as the result of bacterial action (see 
page 71 ) . 

Thin or watery milk is an indication of dilution with 
water or of skimming. Flakes or curds are present in 
milk from an udder affected with mastitis. Other changes 
in consistency are caused by bacteria (see pages 67 and 
69). 

Abnormal odors may be absorbed from the atmos- 
phere or may be caused by bacteria (see pages 29, 30, 
67 and 71). 

A salty or bitter taste is present in mastitis and indi- 
gestion, also near the end of lactation and just before 
parturition. A bitter, metallic taste may be due to rusted 
milk vessels. Milk may also have an abnormal taste 
as a result of the growth of certain bacteria, the absorp- 
tion of gases, and from other causes ( see pages 28 to 30 
and 66 to 71). Heating milk vdll make an abnormal 
odor more pronounced. 



228 



PRINCIPLES AND PRACTICE OF MILK HYGIENE 



DETERMINATION OF SPECIFIC GRAVITY 

The specific gravity of milk is determined by means 
of Quevenne's lactometer (Fig. 31) or modifications of 
this apparatus. 

After being thoroughly mixed, some of the milk to 
be tested is poured into a high glass cylinder and the 
lactometer is slowly and carefully lowered 
into the fluid until it floats. Care should 
be taken not to mix air with the milk. 
This can be avoided by pouring the milk 
against the side of the vessel. The lacto- 
meter must not be permitted to touch 
the side of the cylinder. When the 
lactometer has become stationary, the 
specific gravity is indicated by the 
figures on the scale in the stem of the 
lactometer. The reading is taken from 
the line in the scale which is on a level 
with the surface of the milk. The stem 
of the lactometer draws the milk up 
around it, forming a slight meniscus 
which obscures the line at the surface of 
the milk. The reading should not be 
taken from the top of this meniscus, but 
at the surface of the milk, the depth of 
the meniscus being estimated. The 

Fia, 31. — Quevenne'8 n i i i i 

lactometer. figurcs on thc lactomctcr scale do not ex- 
press the specific gravity but Quevenne degrees. By 
dividing Quevenne degrees by 1000 and adding 1, the 
specific gravity is obtained. 

The temperature of the milk should be 15° C. (60° 
F. ) when the specific gravity is taken, and the tempera- 
ture should be taken with an accurate thermometer after 



METHODS OF EXAMINING MILK 229 

the milk has been placed in the glass cylinder and the 
lactometer introduced. The lactometer reading and the 
temperature should be taken as nearly as possible at 
the same time. If the temperature of the milk is not 
exactly 15° C. (60° F.), then the specific gravity at this 
temperature must be calculated from the lactometer and 
thermometer reading, because this is the standard tem- 
perature. Adding to the specific gravity 0.0002 for each 
degree Centigrade above 15 or 0.0001 for each degree 
Fahrenheit above 60, and subtracting the same numbers 
for each degree below the standard temperature, will 
give the approximate specific gravity at the standard 
temperature ; but more accurate results will be obtained 
by using the tables on pages 230 and 231. If, for exam- 
ple, the lactometer reading is 28 and the temperature is 
17° C, locate 1.028 in the column at the extreme left and 
follow this line to the right to the column headed 17° C. ; 
the figures at this point, 28.4, represent the lactometer 
reading at 15° C. To obtain exact results, the specific 
gravity should be taken with the milk at 15° C, because 
lactometers are calibrated for this temperature. After 
the specific gravity is taken the lactometer should be 
rinsed with water and wiped dry. 

The specific gravity of milk may also be determined 
by means of the Westphal balance (Fig. 32). This in- 
strument consists of a pivoted beam with a float hanging 
from one end. The milk to be tested is placed in a glass 
cj^linder and the float is let down into the milk. The 
weights on the beam are then moved until equilibrium 
is established, and the specific gravity is indicated by the 
position of the weights. 

The specific gravity of normal market milk ranges 
from 1.028 to 1.034, the average being 1.032. Skimming 



230 



PRINCIPLES AND PRACTICE OF MILK HYGIENE 



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METHODS OF EXAMINING MILK 



231 





"1 
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■^ »o d i> 06 d d 

GO 00 eo GO GO GO ^ 






o 

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04 




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GO GO 


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GO GO 


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•*' «5 d «> 06 d d 
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232 



PRINCIPLES AND PRACTICE OF MILK HYGIENE 



off the cream or adding skimmed milk increases the spe- 
cific gravity, while the addition of water decreases it. It 
is not possible to detect these forms of adulteration from 
the change in specific gravity alone, on account of the 
wide range in the specific gravity of normal milk, but 
when considered in connection with the per cent, of fat 
and solids not fat the specific gravity is of great assist- 
ance. The specific gravity of skimmed milk may be 
lowered to normal by the addition of a suitable quantity 
of water. When this is suspected, 
the determination of the specific 
gravity of the dry matter or solids 
and the per cent, of fat in the total 
solids will throw further light on 
the subject. The test for nitrates 
and nitrites will assist in discover- 
ing the addition of water (see page 
247). The refraction number of 
the milk serum is also of value in 
this connection (see page 250) . 

It is necessary to refer to the 
New York Board of Health lac- 
tometer because it is still used to some extent in 
the East, although it is constructed on the incorrect 
theory that 1.029 is the lowest specific gravity of pure 
milk. Its scale is divided into 120 divisions. One hun- 
dred corresponds to 29 Quevenne degrees, or a specific 
gravity of 1.029. Milk testing 90 on this scale is sup- 
posed to be 90 per cent, pure, i.e.^ 10 per cent, of water 
is supposed to have been added, which, of course, is 
not always true. Readings on this scale may be con- 
verted into Quevenne degrees by multiplying by 0.29 
or the following table may be used : 




Fig. 32. — Westphal balance. 
(From Chemical Testing of Milk 
and Cream, by R. H. Shaw, 
U. S. Dept. of Agriculture.) 



METHODS OF EXAMINING MILK 



233 



Board of 


Quevenne 


Board of 


Quevenne 


Board of 


Quevenne 


health degrees 


scale 


health degrees 


scale 


health degrees 


scale 


61 


17-7 


81 


23-5 


101 


28-3 


62 


18-0 


82 


23-8 


102 


29-6 


63 


18-3 


83 


24-1 


103 


29-9 


64 


18-6 


84 


24-4 


104 


30-2 


65 


18-8 


85 


24-6 


105 


30-5 


66 


19-1 


86 


24-9 


106 


SO-7 


67 


19-4 


87 


25-2 


107 


31-0 


68 


19-7 


88 


25-5 


108 


31-3 


69 


20-0 


89 


25-8 


109 


31-6 


70 


20-3 


90 


26-1 


110 


31-9 


71 


20-6 


91 


26-4 


111 


32-2 


72 


20-9 


92 


26-7 


112 


32-5 


73 


21-2 


93 


27-0 


113 


82-8 


74 


21-5 


94 


27-3 


114 


33-1 


76 


21-7 


95 


27-6 


115 


33-4 


76 


22-0 


96 


27-8 


116 


33-6 


77 


22-3 


97 


28-1 


117 


33-9 


78 


22-6 


98 


28-4 


118 


34-2 


79 


22-9 


99 


28-7 


119 


34-5 


80 


23-2 


100 


29-0 


120 


34-8 



DETERMINATION OF THE PER CENT. OF FAT 

Babcock Test. — The method devised by Dr. S. M. 
Babcock is the one most commonly used in the United 
States for determining the per cent, of fat in milk and 
other dairy products. The apparatus required consists 
of a bottle of about 50 c.c. capacity with a long neck 
containing graduations from which the per cent, of fat 
can be read off, a pipette holding 17.6 c.c, and a small 
measuring cylinder graduated to measure 17.5 c.c. A 
centrifuge is also necessary. The graduations on the 
neck of the old type of bottle extend from to 10 per 
cent., with subdivisions of 0.2 per cent., but on the more 
recent type the scale is divided into tenths and extends 
from to 8 per cent. Only glassware should be used 
which has been tested and approved by the United States 
Bureau of Standards. Commercial sulphuric acid with 
a specific gravity of 1.82 to 1.83 at 60° F. is used in 



234 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

making the test. The acid dissolves the solids not fat 
and liberates the fat from its emulsion, generates heat 
which causes the fat globules to run together, and in- 
creases the specific gravity of the serum. The test is 
made as follows: The temperature of the milk should 






i 






Fia.33. — Modern typeof Babcock milk- 
testing bottle conforming to the require- 
ments of the U. S. Bureau of Standards. 
(From Chemical Testing of Milk and 
Cream, by R. H. Shaw, U. S. Dept. of Ag- 
riculture.) 



176 
cc. 

\ / 



Fig. 34. — Pipette used in Babcock 
test for measuring mUk. 'From Chem- 
ical Testing of Milk and Cream, by 
R. H. Shaw, U. S. Dept. of Agriculture.) 



be between 60° and 70° F. After the milk has been 
thoroughly mixed, the tip of the pipette is inserted just 
beneath the surface and filled to the 17.6 c.c. mark. 
The pipette is then inserted obliquely into the mouth of 
the bottle and the milk permitted to run slowly down 
the inside of the neck. When the milk ceases flowing, 
the pipette is blown into to force out any residue. To 



^ — ^ 



175 

CO 



METHODS OF EXAMINING MILK 235 

obtain accurate results, every particle of milk must be 
delivered into the bottle. The measuring cylinder is 
filled to the 17.5 c.c. mark with sulphuric acid; then, 
with the bottle held by the neck in an oblique position, 
the acid is poured slowly down the side, the bottle being 
rotated slowly so that any milk in the neck will be washed 
down. The acid and milk are then mixed by grasping 
the bottle by the neck and gently whirling it, first to the 
right and then to the left, or by holding the bottle by 
the neck in an inclined position with the edge of the bot- 
tom resting on a table and rotating it, 
first in one direction and then in the 
other. When mixing is once com- 
menced it must be continued until 
solution is complete. The solution 
should finally be of a dark brown color. 
The bottle is placed in a centrifuge 
and whirled for five minutes at a speed 
of 800 to 1200 revolutions per minute. 

^ Fig. 35. — Cylinder used 

Hot water at a temperature above in Babcock test for meas- 

J^ uring acid. (P rom Chemi- 

120° F. (49° C.) is then added until ^tamft/ r.' h^" 
the bottle is filled to the bottom of the ' ' ^^*° 2"*='"*''™- 
neck and the bottle is replaced in the centrifuge and 
whirled for two minutes. Hot water is again added until 
the fluid in the bottle is raised to a point near the top 
of the graduated scale, the water being dropped directly 
into the fluid, not run down the side, in order to remove 
any flocculent material which may be entangled in the 
fat at the top. The bottle is then whirled another min- 
ute. After the whirling is completed, the fat should be 
collected at the top of the fluid in the bottle in a column 
of clear, yellowish liquid, with a nearly colorless fluid 
below it. The fat column should have a well-defined 



C3 



236 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

meniscus at the top and bottom, and the reading should 
be made from the bottom of the lower meniscus to the 
top of the upper one. A pair of calipers will be found 
convenient for measuring the fat column. The tem- 
perature of the contents of the bottle should be between 
130° and 140° ,F. (54° to 60° C.) when the reading is 
taken. Foam on the top of the fat column is caused by 
using hard water. Dark colored particles in the fat 
column may be due to several causes: acid too concen- 
trated, too much acid, milk too warm when acid was 
added, allowing acid to mix with milk when placing it 
in the bottle, allowing the bottle to stand too long before 
mixing the acid and milk, and interrupting the mixing 
before the solution was complete. Wliite particles in 
the fat column may result from acid which is too weak, 
too little acid, acid or milk being too cold, and insuffi- 
cient mixing. Immediately after the reading is taken 
the bottle should be emptied, rinsed out twice with boil- 
ing water and placed in a rack to drain. Now and then 
the bottles should be washed in a solution of soap powder 
or in a dilute solution of lye. 

The Babcock test for fat in cream is made in very 
much the same manner as for milk, except that a bottle 
with a longer neck and more extensive graduations is 
used and the cream is weighed instead of measured. 
There are two sizes of bottles, one for 9 grammes and 
the other for 18 grammes of cream. The test bottle is 
placed on the scales and the cream is introduced into the 
bottle with a pipette. Sufficient sulphuric acid is added 
to give the mixture the color of coffee; the quantity 
required will vary with the per cent, of fat in the cream. 
The bottle is then whirled in the centrifuge and water 
added exactly as in testing milk. On being finally re- 



METHODS OF EXAMINING MILK 



237 



moved from the centrifuge, the bottle is placed in water 
ac a temperatm-e of 135° to 140° F. (57° to 60° C.) 
and submerged to a point above the fat column for 15 
minutes, after which the per cent, of fat is read off from 
the scale. The reading is taken from the bottom of the 
lower meniscus to the bottom of the upper one. It is 
recommended that the upper meniscus be destroyed by 
dropping a few drops of glymol 
(liquid petrolatum, white min- 
eral oil) into the test bottle and 
the reading taken from the bot- 
tom of the lower meniscus to 
the line between the glymol and 
the fat. 

Gerher Test.— {¥ig. 36.) 
This test is used almost exclu- 
sively in Europe and to some ex- 
tent in this country. The prin- 
ciple is the same as in the Bab- 
cock test, except that the fat is 
not only liberated from its emul- 
sion by sulphuric acid but is 
also dissolved in amyl alcohol. 
The apparatus required con- 
sists of a special type of bottle 
(G) known as an acido-butyrometer, which has a long 
neck containing a scale graduated in tenths, each division 
representing 0.1 per cent, of fat, and an opening in the 
bottom which may be closed with a rubber stopper ; also 
three pipettes: 1 of 11 c.c. capacity to measure the milk 
(K), an acid pipette holding 10 c.c. (H), and a 1 c.c. 
pipette for the amyl alcohol (I). The chemicals used 
are commercial sulphuric acid of a specific gravity of 




Fig. 36. — Bottle and pipettea used in 

Gerber test. 



238 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

1.825 at 15° C. and amyl alcohol. The test is made as 
follows : The milk and the chemicals should be at a tem- 
perature of 15° C. ; 10 c.c. of sulphuric acid are measured 
with the acid pipette and placed in the bottle. The point 
of the pipette should be passed obliquely through the 
opening of the bottle until it comes in contact with the 
side of the bottle, when the acid is allowed to flow slowly 
out. Care should be taken that no acid is deposited in 
the spiral grooves on the inner side of the opening. After 
thoroughly mixing the milk, 11 c.c. are drawn up into 
the proper pipette and placed in the bottle with the 
same precautions, the milk being permitted to flow 
slowly down the side of the bottle so that it will not mix 
with the acid. Then 1 c.c. of amyl alcohol is placed in 
the bottle in the same manner with the alcohol pipette. 
The three fluids should be arranged in three distinct 
layers. The bottle is closed with the rubber stopper and 
the fluids are mixed by slowly raising first one end of the 
bottle and then the other, permitting the fluid to flow in 
and out of the neck. This is continued until a perfect 
solution is obtained. The rubber stopper should be 
forced in sufficiently to raise the fluid to the zero mark 
on the scale in the neck and it should be held in place 
with the thumb while the bottle is being shaken. This 
latter precaution is taken to prevent the stopper from 
coming out, although this is not likely to occur if it is 
properly inserted. The bottle should be placed in a 
water bath at a temperature of 60° to 65° C. (140° to 
150° F.), with the stopper downward and the water 
covering the entire bottle, until it is centrifugalized. This 
will not be necessary, however, when only one or two 
samples are being tested. If a hand centrifuge is used 
the whirling must be continued 10 minutes, but with a 



METHODS OF EXAMINING MILK 



239 



power machine making 800 to 1000 revolutions per min- 
ute 3 to 4 minutes is sufficient. When the bottles are 
removed from the centrifuge they should be submerged 
in an upright position, with the stopper downward, in 
a water bath at 60° C. (140 ° F.) until the reading is 
taken, unless the samples are so few that they can all be 
read in a few seconds. The fat collects in 
a clear, yellow column at the top of the 
fluid in the neck. The stopper is turned 
sufficiently to bring the lower border of 
the fat column on a level with one of the 
main divisions of the scale and the per 
cent, of fat is then read off. The read- 
ing is taken from the bottom of the fat 
column to the lower border of the menis- 
cus at the top. After the reading is taken 
the bottle should be emptied at once and 
cleaned as directed for the Babcock bottle. 

A special bottle is made for testing 
cream. The cream placed in the bottle is 
weighed; otherwise the per cent, of fat in 
cream is determined in the same manner 
as that in milk. 

Lactoscope Test. — It was proposed 
some time ago to determine the per cent, 
of fat in milk by measuring its transpar- 
ency. Several forms of apparatus have been devised for 
this purpose, the simplest being Feser's lactoscope (Fig. 
37). This is a glass tube, contracted towards the bot- 
tom. A vertical white-glass column, which is encircled 
by six blaek horizontal lines, projects upward into the 
contracted part. On the surface of the upper part of the 
tube there is a graduated scale with a column of figures 



Fig. 37. — Feser's 
lactoscope. 



240 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

at either side, one column representing the capacity in 
cubic centimetres and the other standing for per cent, of 
fat. The test is made as follows : 4 c.c. of the milk to be 
tested are placed in the glass tube and water is added up 
to the line marked 40. The two fluids are mixed and the 
apparatus is then held at arm's length with the back of 
the examiner to the light. If the black lines on the ver- 
tical column can be distinguished, then the figure in the 
per cent, column opposite the line which is on a level with 
the top of the fluid is supposed to represent the per cent, 
of fat. If the black lines are not visible, then water is 
added until the fluid is on a level with the next line on the 
scale and the fluid is mixed by shaking; this is repeated 
until the black lines can be seen, when the per cent, of fat 
is read ofl". This test is inaccurate because the degree of 
opacity of milk is not dependent entirely upon the quan- 
tity of fat but is also influenced by the size of the fat 
globules and by the calcium caseinate (see page 28). 
An error of 0.5 to 1 per cent, in either direction may 
occur in the examination of whole milk and the fat per 
cent, indicated for skim milk is usually too high. 

DETERMINATION OF TOTAL SOLIDS 

Gravimetric Method. — The apparatus required in- 
cludes evaporating dishes, an accurate analytical balance 
with weights, a pipette, a water bath, a hot-water oven, 
and a desiccator. Platinum dishes are the most desirable, 
but porcelain and silica dishes are satisfactory and much 
cheaper; they should have a diameter of not less than 5 
centimetres. 

The dishes are cleaned and dried, placed in the hot- 



METHODS OF EXAMINING MILK 241 

water oven for a half hour, removed to the desiccator 
until cool and then weighed. After they are placed in 
the oven they should be handled with tongs or forceps 
and should not be touched with the fingers. As each 
dish is weighed the weight is recorded. The milk sample 
is mixed thoroughly and some of the milk (3 to 5 c.c.) is 
transferred to the dish, which is again weighed, the 
weight being recorded. The dish is placed on a water 
bath where it remains until the milk is evaporated to 
dryness. It is then removed to the desiccator and when 
cool it is weighed. Following this it is placed in the 
hot-water oven for 30 minutes, after which it is again 
cooled in the desiccator and weighed. If the two weigh- 
ings agree, or are within 0.2 milligramme of each othei-, 
the water has all been driven off. If the weighings do 
not agree to this extent, the dish must be returned to 
the hot-water oven for another period, then placed in the 
desiccator until cool and again weighed, and this must 
be continued until the weight is constant, or within 0.2 
milligramme of being the same. The last weight minus 
the weight of the dish represents the weight of the dry 
matter or total solids in the charge of milk. Multiplying 
the weight of the dry matter by 100 and dividing by the 
weight of the charge will give the per cent, of dry matter 
in milk. The per cent, of ash may be determined by 
heating the dry matter until the ash is free from carbon, 
placing the dish in the desiccator until cool, weighing, 
subtracting the weight of the dish, multiplying the re- 
mainder by 100 and dividing by the weight of the charge. 
By Calculation. — There are several formulas for 
calculating the total solids and solids not fat from the 
specific gravity and per cent, of fat. Of these Babcock's 
16 



242 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



formula gives the most accurate results when compared 
with gravimetric determinations. This formula is as 
follows : 

Per cent, solids not fat=(^^5^^=^-A X (100 -f) 2.5 



l OOS-Sf 
10-1.0753 £ 

S = specific gravity; f=per cent, of fat. 



The results obtained with this formula will not differ 
more than 0.25 to 0,5 per cent, from those obtained by 
the gravimetric method. A table prepared by Shaw and 
Eckles, which renders it unnecessary to make the cal- 
culation for each sample, will be found on pages 243 to 
245. The Babcock formula determines the per cent, of 
solids not fat, but this table gives the per cent, of total 
solids ; it is a modification of one prepared by Dr. Bab- 
cock. In the table the per cent, of total solids in any 
given sample will be found at the intersection of the 
column headed by the number representing the lactom- 
eter reading (Quevenne degrees) and the line corre- 
sponding to the fat per cent., provided the lactometer 
reading is a whole number. If the lactometer reading is 
not a whole number then the per cent, of total solids is 
found for the whole number and to this is added the 
fraction found opposite the decimal in the table for 
" proportional parts." Take, for example, a sample of 
milk with a lactometer reading of 33.5 and a fat per 
cent, of 3.5. At the point where the column headed 33 
and the line marked 3.5 per cent, fat intersect are the 
figures 12.46. In the table for " proportional parts," 
opposite the decimal .5 is the fraction .13. This added 
to 12.46 equals 12.59, which represents the per cent, of 
total solids. 



Table fob Determining Total, Solids in Milk From Ant Given Specific 
Gravity and Percentage of Fat 



Per- 
cent- 
age of 


Lactometer reading at 60° F. (Quevenne degrees) 


fat 


26 


27 


28 1 29 


30 


31 


32 


33 


34 


35 36 




Per 


Per 


Per 


Per 


Per 


Per 


Per 


Per 


Per 


Per Per 




cent. 


cent. 


cent. 


cent. 


cent. 


cent. 


cent. 


cent. 


cent. 


cent. 


cent. 




total 


total 


total 


total 


total 


total 


total 


total 


total 


total 


total 




solids 


solids 


solids 


solids 


solids 


solids 


solids 


solids 


solids 


solids 


solids 


2.00 


8.90 


9.15 


9.40 


9.65 


9.90 


10.15 


10.40 


10.66 


10.91 


11.16 


11.41 


2.05 


8.96 


9.21 


9.46 


9.71 


9.96 


10.21 


10.46 


10.72 


10.97 


11.22 


11.47 


2.10 


9.02 


9.27 


9.52 


9.77 


10.02 


10.27 


10.52 


10.78 


11.03 


11.28 


11.53 


2.15 


9.08 


9.33 


9.58 


9.83 


10.08 


10.33 


10.58 


10.84 


11.09 


11.34 


11.59 


2.20 


9.14 


9.39 


9.64 


9.89 


10.14 


10.39 


10.64 


10.90 


11.15 


11.40 


11.65 


2.25 


9.20 


9.45 


9.70 


9.95 


10.20 


10.45 


10.70 


10.96 


11.21 


11.46 


11.71 


2.30 


9.26 


9.51 


9.76 


10.01 


10.26 


10.51 


10.76 


11.02 


11.27 


11.52 


11.77 


2.35 


9.32 


9.57 


9.82 


10.07 


10.32 


10.57 


10.82 


11.08 


11.33 


11.58 


11.83 


2.40 


9.38 


9.63 


9.88 


10.13 


10.38 


10.63 


10.88 


11.14 


11.39 


11.64 


11.89 


2.45 


9.44 


9.69 


9.94 


10.19 


10.44 


10.69 


10.94 


11.20 


11.45 


11.70 


11.95 


2.50 


9.50 


9.75 


10.00 


10.25 


10.50 


10.75 


11.00 


11.20 


11.51 


11.76 


12.01 


2.55 


9.56 


9.81 


10.06 


10.31 


10.56 


10.81 


11.06 


11.32 


11.57 


11.82 


12.07 


2.60 


9.62 


9.87 


10.12 


10.37 


10.62 


10.87 


11.12 


11.38 


11.63 


11.88 


12.13 


2.65 


9.68 


9.93 


10.18 


10.43 


10.68 


10.93 


11.18 


11.44 


11.69 


11.94 


12.19 


2.70 


9.74 


9.99 


10.24 


10.49 


10.74 


10.99 


11.24 


11.50 


11.75 


12.00 


12.25 


2.75 


9.80 


10.05 


10.30 


10.55 


10.80 


11.05 


11.31 


11.56 


11.81 


12.06 


12.31 


2.80 


9.86 


10.11 


10.36 


10.61 


10.86 


11.11 


11.37 


11.62 


11.87 


12.12 


12.37 


2.85 


9.92 


10.17 


10.42 


10.67 


10.92 


11.17 


11.43 


11.68 


11.93 


12.18 


12.43 


2.90 


9.98 


10.23 


10.48 


10.73 


10.98 


11.23 


11.49 


11.74 


11.99 


12.24 


12.49 


2.95 


10.04 


10.29 


10.54 


10.79 


11.04 


11.30 


11.55 


11.80 


12.05 


12.30 


12.55 


3.00 


10.10 


10.35 


10.60 


10.85 


11.10 


11.36 


11.61 


11.86 


12.11 


12.36 


12.61 


3.05 


10.16 


10.41 


10.66 


10.91 


11.17 


11.42 


11.67 


11.92 


12.17 


12.42 


12.68 


3.10 


10.22 


10.47 


10.72 


10.97 


11.23 


11.48 


11.73 


11.98 


12.23 


12.48 


12.74 


3.15 


10.28 


10.53 


10.78 


11.03 


11.29 


11.54 


11.79 


12.04 


12.29 


12.55 


12.80 


3.20 


10.34 


10.59 


10.84 


11.09 


11.35 


11.60 


11.85 


12.10 


12.35 


12.61 


12.86 


3.25 


10.40 


10.65 


10.90 


11.16 


11.41 


11.66 


11.91 


12.16 


12.42 


12.67 


12.92 


3.30 


10.46 


10.71 


10.96 


11.22 


11.47 


11.72 


11.97 


12.22 


12.48 


12.73 


12.98 


3.35 


10.52 


10.77 


11.03 


11.28 


11.53 


11.78 


12.03 


12.28 


12.54 


12.79 


13.04 


3.40 


10.58 


10.83 


11.09 


11.34 


11.59 


11.84 


12.09 


12.34 


12.60 


12.85 


13.10 


3.45 


10.64 


10.89 


11.15 


11.40 


11.65 


11.90 


12.15 


12.40 


12.66 


12.91 


13.16 


3.50 


10.70 


10.95 


11.21 


11.46 


11.71 


11.96 


12.21 


12.46 


12.72 


12.97 


13.22 


3.55 


10.76 


11.02 


11.27 


11.52 


11.77 


12.02 


12.27 


12.52 


12.78 


13.03 


13.28 


3.60 


10.82 


11.08 


11.33 


11.58 


11.83 


12.08 


12.33 


12.58 


12.84 


13.09 


13.34 


3.65 


10.88 


11.14 


11.39 


11.64 


11.89 


12.14 


12.39 


12.64 


12.90 


13.15 


13.40 


3.70 


10.94 


11.20 


11.45 


11.70 


11.95 


12.20 


12.45 


12.70 


12.96 


13.21 


13.46 


3.75 


11.00 


11.26 


11.51 


11.76 


12.01 


12.26 


12.51 


12.76 


13.02 


13.27 


13.52 


3.80 


11.06 


11.32 


11.57 


11.82 


12.07 


12.32 


12.57 


12.82 


13.08 


13.33 


13.58 


3.85 


11.12 


11.38 


11.63 


11.88 


12.13 


12.38 


12.63 


12.88 


13.14 


13.39 


13.64 


3.90 


11.18 


11.44 


11.69 


11.94 


12.19 


12.44 


12.69 


12.94 


13.20 


13.45 


13.70 


3.95 


11.24 


11.50 


11.75 


12.00 


12.25 


12.50 


12.75 


13.00 


13.26 


13.51 


13.77 


4.00 


11.30 


11.56 


11.81 


12.06 


12.31 


12.56 


12.81 


13.06 


13.32 


13.57 


13.83 


4.05 


11.36 


11.62 


11.87 


12.12 


12.37 


12.62 


12.87 13.12 1 13.38 | 


13.63 


13.89 


4.10 


11.42 


11.68 


11.93 


12.18 


12.43 


12.68 


12.93 


13.18 


13.44 


13.69 


13.95 


4.15 


11.48 


11.74 


11.99 


12.24 


12.49 


12.74 


12.99 


13.25 


13.50 


13.76 


14.01 


4.20 


11.54 


11.80 


12.05 


12.30 


12.55 


12.80 


13.05 


13.31 


13.56 


13.82 


14.07 


4.25 


11.60 


11.86 


12.11 


12.36 


12.61 


12.86 


13.12 


13.37 


13.62 


13.88 


14.13 


4.30 


11.66 


11.92 12.17 


12.42 


12.67 


12.92 


13.18 


13.43 


13.68 


13.94 


14.19 


4.35 


11.72 


11.98 


12.23 


12.48 


12.73 


12.98 


13.24 


13.49 


13.74 


14.00 


14.25 


4.40 


11.78 


12.04 


12.29 12.54 


12.79 


13.04 


13.30 


13.55 


13.80 


14.06 


14.31 


4.45 


11.84 


12.10 


12.35 12.60 


12.85 


13.10 


13.36 


13.61 


13.86 


14.12 


14.37 



Table fob Determining Total Solids in Milk Fbom Ant Given Specific 
GiLiviTY and Percentage of Fat — Continued 



Per 
cent- 
age of 

fat 






Lactometer reading 


at 60° F 


. (Quevenne degrees). 






26 


27 


28 


23 


30 


31 


32 


83 I 34 


35 


36 




Per 


Per 


Per 


Per 


Per 


Per 


Per 


Per 


Per 


Per 


Per 




cent. 


cent. 


cent. 


cent. 


cent. 


cent. 


cent. 


cent. 


cent. 


cent. 


cent. 




total 


total 


total 


total 


total 


total 


total 


total 


total 


total 


total 




solids 


solids 


solids 


solids 


solids 


solids 


solids 


solids 


solids 


solids 


solids 


4.50 


11.90 


12.16 


12.41 


12.66 


12.91 


13.16 


13.42 


13.67 


13.92 


14.18 


14.43 


4.55 


11.97 


12.22 


12.47 


12.72 


12.97 


13.22 


13.48 


13.73 


13.98 


14.24 


14.49 


4.60 


12.03 


12.28 


12.53 


12.78 


13.03 


13.28 


13.54 


13.79 


14.04 


14.30 


14.55 


4.65 


12.09 


12.34 


12.59 


12.84 


13.09 


13.34 


13.60 


13.85 


14.10 


14.36 


14.61 


4.70 


12.15 


12.40 


12.65 


12.90 


13.15 


13.40 


13.66 


13.91 


14.16 


14.42 


11.67 


4.75 


12.21 


12.46 


12.71 


12.96 


13.21 


13.46 


13.72 


13.97 


14.22 


14.48 


14.73 


4.80 


12.27 


12.52 


12.77 


13.02 


13.27 


13.52 


13.78 


14.03 


14.28 


14.54 


14.79 


4.85 


12.33 


12.58 


12.83 


13.08 


13.33 


13.58 


13.84 


14.09 


14.34 


14.60 


14.85 


4.90 


12.39 


12.64 


12.89 


13.^4 


13.39 


13.64 


13.90 


14.15 


14.40 


14.66 


14.91 


4.95 


12.45 


12.70 


12.95 


13.20 


13.45 


13.70 


13.96 


14.21 


14.46 


14.72 


14.97 


6.00 


12.51 


12.76 


13.01 


13.26 


13.51 


13.76 


14.02 


14.27 


14.52 


14.78 


15.03 


6.05 


12.57 


12.82 


13.07 


13.32 


13.57 


13.83 


14.08 


14.33 


14.58 


14.84 


15.09 


6.10 


12.63 


12.88 


13.13 


13.38 


13.63 


13.89 


14.14 


14.39 


14.64 


14.90 


15,15 


6.15 


12.69 


12.94 


13.19 


13.44 


13.69 


13.95 


14.20 


14.45 


14.70 


14.96 


15.21 


6.20 


12.75 


13.00 


13.25 


13.50 


13.75 


14.01 


14.26 


14.51 


14.76 


15.02 


15.27 


5.25 


12.81 


13.06 


13.31 


13.56 


13.81 


14.07 


14.32 


14.57 


14.82 


15.08 


15.33 


5.30 


12.87 


13.12 


13.37 


13.62 


13 87 


14.13 


14.38 


14.63 


14.88 


15.14 


15.39 


5.35 


12.93 


13.18 


13.43 


13.68 


13.93 


14.19 


14.44 


14.70 


14.95 


15.20 


15.45 


6.40 


12.99 


13.24 


13.49 


13.74 


14.00 


14.25 


14.50 


14.76 


15.01 


15.26 


15.61 


5.45 


13.05 


13.30 


13.55 


13.80 


14.06 


14.31 


14.56 


14.82 


15.07 


15.32 


15.57 


6.50 


13.11 


13.36 


13.61 


13.86 


14.12 


14.37 


14.62 


14.88 


15.13 


15.38 


16.63 


5.55 


13.17 


13.42 


13.67 


13.93 


14.18 


14.43 


14.69 


14.94 


15.19 


15.44 


15.69 


6.60 


13.23 


13.48 


13.73 


13.99 


14.24 


14.49 


14.75 


15.00 


15.25 


15.50 


16.75 


6.65 


13.29 


13.54 


13.79 


14.05 


14.30 


14.55 


14.81 


15.06 


15.31 


15.56 


15.81 


5.70 


13.35 


13.60 


13.85 


14.11 


14.36 


14.61 


14.87 


15.12 


15.37 


15.62 


15.87 


6.75 


13.41 


13.66 


13.91 


14.17 


14.42 


14.68 


14.93 


15.18 


15.43 


15.68 


15.93 


6.80 


13.47 


13.72 


13.97 


14.23 


14.48 


14.74 


14.99 


15.24 


15.49 


15.74 


15.99 


6.85 


13.53 


13.78 


14.04 


14.29 


14.54 


14.80 


15.05 


15.30 


15.55 


15.80 


16.06 


6.90 


13.59 


13.84 


14.10 


14.35 


14.60 


14.86 


15.11 


15.36 


15.61 


15.86 


16.12 


5.95 


13.65 


13.90 


14.16 


14.41 


14.66 


14.92 


15.17 


15.42 


15.67 


15.92 


16.18 


6.00 


13.71 


13.96 


14.22 


14.47 


14.72 


14.98 


15.23 


15.48 


15.73 


15.98 


16.24 


6.05 


13.77 


14.02 


14.28 


14.53 


14.78 


15.04 


15.29 


15.54 


15.79 


16.04 


16.30 


6.10 


13.83 


14.08 


14.34 


14.59 


14.84 


15.10 


15.35 


15.60 


15.85 


16.10 


16.35 


6.15 


13.89 


14.14 


14.40 


14.65 


14.90 


15.16 


15.41 


15.66 


15.91 


16.16 


16.42 


6.20 


13.95 


14.20 


14.46 


14.71 


14.96 


15.22 


15.47 


15.72 


15.97 


16.22 


16.48 


6.25 


14.01 


14.26 


14.52 


14.77 


15.02 


15.28 


15.53 


15.78 


16.03 


16.28 


16.54 


6.30 


14.07 


14.32 


14.58 


14.83 


15.08 


15.34 


15.59 


15.84 


16.09 


16.34 


16.60 


6.35 


14.13 


14.38 


14.64 


14.90 


15.14 


15.40 


15.65 


15.90 


16.15 


16.40 


16.66 


6.40 


14.19 


14.44 


14.70 


14.96, 


15.20 


15.46 


15.71 


15.96 


16.21 


16.46 


16.72 


6.45 


14.25 


14.50 


14.76 


15.02 


15.26 


15.52 


15.77 


16.02 


16.27 


16.52 


16.78 


6.50 


14.31 


14.56 


14.82 


15.08 


15.32 


15.58 


15.83 


16.08 


16.33 


16.58 


16.84 


6.55 


14.37 


14.62 


14.88 


15.14 


15.38 


15.64 


15.89 


16.14 


16.39 


16.64 


16.90 


6.60 


14.43 


14.68 


14.94 


15.20 


15.44 


15.70 


15.95 


16.20 


16.45 


16.70 


16.96 


6.65 


14.49 


14.74 


15.00 


15.26 


15.50 


15.76 


16.01 


16.26 


16.51 


16.76 


17.02 


6.70 


14.55 


14.80 


15.06 


15.32 


15.56 


15.82 


16.07 


16.32 


16.57 


16.82 


17.08 


6.75 


14.61 


14.86 


15.12 


15.38 


15.62 


15.88 


16.13 


16.38 


16.63 


16.88 


17.14 


6.80 


14.67 


14.92 


15.18 


15.44 


15.68 


15.94 


16.19 


16.44 


16.69 


16.94 


17.20 


6.85 


14.73 


14.98 


15.24 


15.50 


15-74 


16.00 16.25 


16.50 


16.75 


17.00 


17.26 


6.90 


14.79 


15.04 


15.30 


15.56 


15.80 


16.06 16.31 


16.56 


16.81 


17.06 


17.32 


6.95 


14.85 


15.10 


15.36 


15.62 


15.86 


16.12 16.37 


16.62 16.87! 


17.12 1 


17.38 



METHODS OF EXAMINING MILK 

PBOPORTIONAL PABTS 



245 



Lactometer 
fraction 


Fraction to 

be added 

to total 

eolids 


Lactometer 
fraction 


Fraction to 

be added 

to total 

solids 


Lactometer 
fraction 


Fraction to 

be added 

to total 

solids 


0.1 

.2 
.3 


0.03 
.05 

.08 


0.4 
.6 

.6 


0.10 
.13 
.15 


0.7 
.8 
.9 


0.18 
.20 
.23 



A simpler but less accurate formula by Babcock is 
based on the fact that the per cent, of total solids in- 
creases at about the rate of 0.25 for each lactometer 
(Quevenne) degree and 1.2 for each per cent, of fat. 
This formula is as follows. 

Per cent, total solids = ^ L +(!•!« f) 

L =» lactometer reading (Quevenne degrees) ; £ = fat per cent. 

By Automatic Reckoner. — The per cent, of total 
solids can also be determined, when the specific gravity 
and fat per cent, are known, by means of Ackermann's 
automatic reckoner and Richmond's sliding rule. The 
former is based upon Fleischmann's formula and the 
latter upon Richmond's formula. These two formulas 
do not give quite as accurate results as the Babcock for- 
mula on page 242. 



DETERMINATION OF SOLIDS NOT FAT 

When the per cent, of fat and of total solids is 
known, the per cent, of solids not fat can be determined 
by simply subtracting the per cent, of fat from the per 
cent, of total solids. The per cent, of solids not fat can 
also be closely calculated from the fat per cent, and the 
specific gravity by means of Babcock's formula (page 
242 ) . The per cent, of solids not fat in normal market 
milk ranges from 8.5 to 10.5. 



246 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
DETERMINATION OF THE SPECIFIC GRAVITY OF THE SOLIDS 

The specific gravity of the dry milk solids can be cal- 
culated from the per cent, of total solids and the specific 
gravity of the milk according to the following formula: 

St 

™~st-(100s-100) 
m represents dry milk solids, s speci6c gravity and t total solids. 

The specific gravity of the dry solids of normal whole 
milk varies from 1.31 to 1.36. Skimming milk increases 
the specific gravity of the milk solids. 

DETERMINATION OF THE PER CENT. OF FAT IN THE 
TOTAL SOLIDS 

The per cent, of fat in the total solids can be calcu- 
lated from the per cent, of fat and of total solids in the 
milk according to the following formula : 

p = ^X100 

p represents per cent, of fat in total solids, f per cent, of fat in the milk and 
t per cent, of total solids. 

The per cent, of fat in the total solids varies from 
20 to 34. It is decreased by skimming. 

DETERMINATION OF THE DEGREE OF ADULTERATION 

When it is possible to compare a sample of adulter- 
ated milk with a sample of the same milk collected under 
conditions which exclude the possibility of adulteration, 
the extent of the adulteration may be determined approxi- 
mately by the following formulas of Bohmlander: 

M=— Xw-W 

r 



E = 100 



0-i) 



METHODS OF EXAMINING MILK 247 

In the first formula W is the per cent, of water in 
the unadulterated sample; w is the per cent, of water 
in the adulterated sample; R is the per cent, of solids 
not fat in the unadulterated sample ; r is the per cent, of 
solids not fat in the adulterated sample; M represents 
the quantity of water to 100 grammes of milk. 

In the second formula F is the per cent, of fat in the 
unadulterated sample; f is the per cent, of fat in the 
adulterated sample; R is the per cent, of solids not fat 
in the unadulterated sample; r is the per cent, of solids 
not fat in the adulterated sample, and E represents the 
per cent, of fat removed by skimming. 

TESTS FOR NITRATES AND NITRITES 

Soochlet's Test. — One-half c.c. of a 20 per cent, cal- 
cium chloride solution is mixed with about 30 c.c. of milk 
and the mixture is boiled and filtered. A 2 per cent, 
solution of diphenylamin in chemically pure sulphuric 
acid is added in sufficient quantity to some of the filtrate 
to make it milky. Chemically pure sulphuric acid is then 
poured slowly down the side of the test tube so that it 
forms a layer at the bottom. If nitrates or nitrites are 
present a blue zone is formed at the point where the two 
fluids come in contact. This test will detect one part of 
nitrates in 100,000; most farm water contains one part 
in 10,000 (Jensen). 

A modification of this test is described by Rievel as 
follows : Place a small quantity of milk in a test tube and 
then pour in slowly, so that the two fluids will not mix, 
a solution of diphenylamin in chemically pure sulphuric 
acid (1 : 10). If minute traces of nitrites are present a 
blue ring will form at the point of contact of the two 
fluids. 



248 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Fritzmann's Method. — Place 2 c.c. of milk in a test 
tube and slowly run down the side 2 c.c. of pure sul- 
phuric acid to which one drop of a dilute formalin solu- 
tion has been added. In the presence of nitrites a blue- 
violet ring will form at the point of contact of the two 
fluids, but the reaction will not occur in the presence of 
albumen. According to Riegel a suitable formalin solu- 
tion may be made by adding one drop of 40 per cent, 
formalin to 300 c.c of distilled water and mixing 15 
grammes of this solution with one litre of concentrated 
sulphuric acid. This method gives very accurate results 
and is easily carried out (Rievel). 

Fresh, clean milk does not contain nitrites. Ac- 
cording to Jensen, nitrites are not present in the milk 
even when they have been contained in the food or drink- 
ing water of the cow. Marcus and Huyge assert that if 
nitrate of potassium is administered to the cow in quan- 
tities of 5 to 10 grammes the milk sometimes contains 
nitrates. It would seem likely that nitrates would also 
be excreted through the udder if the cow obtained access 
to fertilizer containing nitrates or to sacks which had con- 
tained such fertilizer. 

The demonstration of nitrates or nitrites in milk is 
generally regarded as evidence that water has been added 
to the milk. Most farm waters contain nitrates and 
nitrites, as do also some city water supplies. But Rievel 
points out that the presence of nitrates or nitrites in milk 
cannot be regarded as positive proof that the milk has 
been watered, because when milk vessels are merely 
rinsed with water containing nitrates or nitrites the milk 
may give a positive reaction if the water is quite rich in 
nitrates or nitrites. Tillmans says that normal milk may 



METHODS OF EXAMINING MILK 



249 



contain up to 1 to 2 mg. per litre from this source. Rievel 
also states that a positive reaction may occur with milk 
soiled with manure, but Tillmans has never found dirty 
milk to give any indication of containing more nitrates 
or nitrites than milk from vessels that had been washed 
with water rich in nitrates or nitrites. A negative reac- 
tion to the nitrate test is no evidence that the milk has not 
been watered, as water free from these substances may 
be used for dilution. According to Utz, milk to be 
tested for nitrates should be boiled unless the test can 
be made at once, because the action of the lactic acid- 
forming bacteria may reduce the nitrates or cause them 
to disappear entirely. 

DETECTION OF THE USUAL ADULTERATIONS 

When milk is adulterated, it is usually by partial 
skimming, dilution with skinmied milk, or dilution with 
water. The changes caused by these various forms of 
adulteration are shown in the following table, which is 
taken from Jensen's Milk Hygiene: 



Specific 

gravity 

of the 

milk 



Per- 
centage 
of fat 



Percent- 
age of 
solids 
not fat 



Specific 
gravity 
of the 

milk 

solids 



Per- 
centage 
of fat 
in the 

total 
solids 



Per- 
centage 
of ash 



Presence 
or absence 
of nitrate 



Normal milk 

Skimmed or diluted f 
with skimmed milk^ 

Water added 

Skimmed and water 
added 



1.029 to 
1.034 
aver. 
1.032 

Higher 

Lower 

Little 
change 



3 to 5 

Lower 
Lower 
Lower 



8.5 to 
10.5 

Very 
slightly 
higher 

Lower 



Lower 



1.30 to 
1.34 



Higher 

No 
change 

Higher 



20 to 
34 



Lower 

No 
change 

Lower 



0.7 to 
0.75 



Higher 
Lower 
Lower 





-f- orO 
-j- or 



250 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

Starch, flour, viscogen, etc., may be added to skimmed 
milk or cream to increase the viscosity (see page 33) . 

The test for starch is made as follows: Add a few 
drops of acetic acid to the milk or cream, boil and filter. 
To the filtrate add a few drops of a dilute iodine solution. 
If starch is present the filtrate becomes blue. 

The presence of viscogen is indicated by a high per 
cent, of salts. 

DETERMINATION OF THE REFRACTION NUMBER 

The most satisfactory milk serum for this test is ob- 
tained by Ackermann's calcium chloride method and the 
refractive index is most conveniently determined by 
Zeiss' dipping ref ractometer. The method is as follows : 

30 c.c. of the milk to be tested is placed in a test 
tube of 75 c.c. capacity and mixed with 0.25 c.c. of a 
1 to 10 solution of calcium chloride in distilled water 
(specific gravity 1.1375 and refraction number 26 at 
17.5° C). The test tube is closed with a perforated 
rubber stopper, then connected with a 22 c.c. condenser 
and heated for 15 minutes in a bath of briskly boiling 
water.^ It is then placed in cold water and cooled. Dur- 
ing this process the serum separates from the curd and is 
poured off into a beaker. If the serum is not sufficiently 
free of coagula to permit of the passage of adequate 
light, it is an indication that acid fermentation has ad- 
vanced too far for the milk to be investigated with the 
refractometer, the loss of lactose suffered in such cases 
being sufficient to render the result inaccurate. The 
beaker containing the serum is placed in the water bath 

^ If the milk tube is not connected with a condenser the 
result of the test will be nearly, if not exactly, the same and 
the test is much simplified. 



METHODS OF EXAMINING MILK 



251 



of the refractometer. The temperature of the water 
bath should be 17.5° C. After allowing 8 to 10 minutes 
for the serum in the beaker to reach the same tempera- 
ture, the prism of the refractometer is inserted in the 
beaker and the refraction number is read from the scale, 




FiQ. 38. — Zeiss dipping refractometer. 

which is located in the refractometer beneath the ocular. 
On looking into the ocular it will be observed that a por- 
tion of the field is dark and the remainder light. The 
border line is usually fringed with colors and the com- 
pensator must then be rotated by means of the milled 



252 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

ring on the barrel of the refractometer until the line of 
demarcation between the dark and light areas is sharply 
defined and colorless. When this line falls on one of the 
divisions of the scale it is merely necessary to note the 
number, which is then the refraction number. When the 
line falls between two divisions of the scale the scale is 
then moved towards the border line by turning the thumb 
screw of the micrometer below the ocular until the scale 
division which was nearest to the border line on the dark 
side is exactly on it. The figure opposite the indicator 
on the micrometer is then noted and is added to the 
figure of the scale division as a decimal. For example, 
if the figure opposite the scale division nearest to the 
border line on the dark side was 38 and the micrometer 
was rotated to 7 in moving the scale division to the 
border line, then the refraction number is 38.7 The 
refraction number can be converted into the refractive 
index by means of a formula furnished with the refrac- 
tometer, but this is not necessary. 

Before beginning the examination of a number of 
samples of milk, the refractometer should be tested with 
distilled water, which at 17.5° C. should give a reading 
of 15.5. The water bath is made to hold 12 beakers 
at one time so that when a nimiber of samples are to 
be examined there will be an opportunity for each one 
to reach the required temperature without delaying the 
examinations. When the prism of the refractometer is 
removed from one sample, or from the distilled water, 
it should be wiped dry with a soft linen cloth before being 
introduced into another. 

The refraction number of normal market milk is in 
most cases between 38 and 40.5. In rare cases it may 
be as low as 37.3 and in one case reported by Mai and 



METOHDS OF EXAMINING MILK 253 

Rothenfusser it reached 41.5. The addition of a small 
quantity of water to milk lowers the refraction number, 
but on account of the wide range in the refraction number 
of normal market milk it is necessary, in order to detect 
slight additions of water, to have the herd under suspicion 
milked under supervision and to take a sample of the 
milk and compare the refraction number of this sample 
with the refraction number of the sample of market milk. 
The daily variation in the refraction number of the milk 
of a herd will not exceed 0.1 to 0.55. Changes of feed 
have only a slight influence and incomplete milking has 
no effect. When the refraction number is as low as 36.5 
or below the milk may be unhesitatingly pronounced 
watered. 

The refraction number is not affected by the per 
cent, of fat. A sample of milk taken from the top of a 
can and one taken from the bottom of the same can will 
both have exactly the same refraction number, although 
there will be a great difference in the fat per cent. This is 
an important advantage, because when a charge that milk 
has been watered is based on the specific gi^avity and fat 
per cent, the claim is often made that the sample was 
taken from the bottom of the can or after the top milk 
had been sold. 

The presence of boric acid and borax in the propor- 
tion usuallj^ used to preserve milk (0.1 to 0.2 per cent.) 
will increase the refraction of the milk serum. Salicylic 
acid also increases the refraction when present in as 
small amount as 0.05 per cent, which is the quantity used 
as a preservative, but formaldehj^de causes no increase 
when present in the amount ordinarily used as a preserva- 
tive. Sodium bicarbonate does not have any effect when 
added up to 0.1 per cent. 



254 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

In individual milk from diseased cows the refraction 
number has been found to be decreased in tuberculosis, 
febrile diseases, foot and mouth disease, and mastitis. In 
some cases of streptococcic mastitis Obladen found it as 
low as 24.8. The effect of mixing milk from diseased 
cows with normal milk has not been determined, but since 
diseased milk and watered milk are both low in refraction 
there is a possibility of confusion unless a proper investi- 
gation is made. 

DETERMINATION OF THE REACTION 

Litmus Test. — A strip of red and a strip of blue lit- 
mus paper are dipped in the milk for a few seconds and 
the color of the wet and dry portions is compared. Nor- 
mal milk, when drawn from the udder, is amphoteric to 
litmus, i.e., the blue litmus is changed to red and the red 
litmus to blue. If the milk is more acid than normal, the 
blue paper will be colored red but the red paper will not 
be changed, while if the alkalinity is increased the red 
paper will be colored blue and the blue paper will not 
be changed. Individual milk is frequently alkaline to 
litmus in the last stages of lactation; it also gives an 
alkaline reaction in most cases of mastitis, but in some 
cases it is acid. Market milk is usually acid to litmus ; it 
is never alkaline except when an alkali has been added. 
The litmus test is only of value as a preliminary test 
for individual milk. 

Mann's Acidity Test. — ^The apparatus required for 
this test is a 50 c.c. burette with a stopcock, a stand, a 
beaker or a white cup, a stirring rod, and a 50 c.c. pipette. 
The reagents required are a solution of phenolphthalein 
and a one-tenth normal solution of sodium hydroxide. 
The phenolphthalein solution is prepared by dissolving 



METHODS OF EXAMINING MILK 255 

10 grammes of powdered phenolphthalein in 300 e.c. of 
90 per cent, alcohol. The one-tenth normal (Vio) solu- 
tion of sodium hydroxide (NaOH) should be prepared 
and standardized as directed by the U. S. Pharmacopoeia. 
Each cubic centimetre of this solution contains sufficient 
sodium hydroxide (0,004! granmie) to neutralize 0.009 
gi'anmie of lactic acid. 

After thoroughly mixing the milk or cream to be 
tested, 50 c.c. are measured into the beaker or cup with 
the pipette. The pipette is then filled to the 50 c.c. mark 
with water, preferably distilled, which is added to the 
milk or cream. This is done for the pm-pose of rinsing 
all milk or cream from the pipette. Five to ten drops of 
the phenolphthalein solution are then placed in the beaker 
or cup and the fluid is mixed by stirring with a glass rod. 
The tenth normal sodium hydroxide solution is run into 
the beaker or cup drop by drop, stirring frequently, until 
a pink color appears and remains permanently. The 
amount of sodium hydroxide solution used is then read 
off from the burette. 

The result of the test may be expressed in degrees 
or in per cent of acidity. Degrees of acidity correspond 
to the number of c.c. of tenth-normal sodium hydroxide 
solution used to the hundred c.c. of milk or cream. The 
per cent, of acidity may be obtained by the following 
calculation : 

No. c.c. yiONaOH used X 0^09 ^ ^^^ ^ ^^^^ ^^.^^^ 
No. c.c. milk or cream used 

For example, if 9 c.c. of the one-tenth normal solu- 
tion are used in testing 50 c.c. of milk or cream, then 

^ ^ ^-^^ X 100 = 9 X 0.018 = 0.16 per cent, acidity. 
50 



256 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

If the reaction is alkaline, i.e., if the milk or cream 
becomes permanently pink when the phenolphthalein 
solution is added, or if the pink color appears and remains 
before the addition of the quantity of tenth-normal 
sodium hydroxide solution required for normal milk, then 
the rosolic acid test for alkalies should be applied (see 
page 260). 

Acidity/ Test With Babcock Pipette. — The test for 
acidity may also bt made by using a Babcock fat-test 
pipette to measure the milk or cream. 17.6 c.c. of milk 
or cream is placed in the cup or beaker, a few drops of 
the phenolphthalein solution added and the tenth-normal 
solution of sodium hydroxide run in slowly until the pink 
color appears and remains permanently. The per cent, 
of acid may be determined by dividing the number of c.c. 
of tenth-normal sodium hydroxide solution used by two, 
and expressing the quotient in tenths, thus: 

6 -T- 2 = 3, or 0.3 per cent. acid. 

Farringtonfs Alkaline Tablet Test. — The special 
feature of this test is the use of tablets of sodium car- 
bonate for making the alkaline solution. Each tablet 
contains sufficient alkali to neutralize 0.034 gramme of 
acid. Five tablets are placed in a 100 c.c. graduated 
cylinder and clean, soft water, preferably distilled, is 
added up to the 97 c.c. mark. The cylinder is then 
closed tightly with a stopper and laid on its side for sev- 
eral hours to give the tablets an opportunity to dissolve. 
Solution is never entirely complete, a slight flocculent 
residue remaining. After thoroughly mixing by shaking, 
17.6 c.c. of the milk or cream to be tested is measured 
into the beaker or cup with a Babcock fat-test pipette. 
The pipette is then filled with water to the 17.6 mark 



METHODS OF EXAMINING MILK 257 

to rinse it and this is added to the milk or cream. A few 
drops of phenolphthalein solution are added and the 
alkali solution in the cylinder, after thorough shaking, 
is added to the mixture in the cup or beaker until the 
pink color remains permanent. The number of c.c. used 
is then read off from the measuring cylinder. Each c.c. 
represents one-tenth per cent, of acid in the sample 
tested. 

TESTS FOR PRESERVATIVES 

The use of antiseptics to inhibit bacterial growth and 
thus prevent the souring or decomposition of milk is 
much less common than formerly, but is still practised 
to some extent. This is also true of the addition of 
alkalies to neutralize acidity and delay curdling. Not 
only may the antiseptics do harm themselves, but they 
and the alkalies conceal conditions in milk which are un- 
desirable and may prove injurious. For these reasons, 
the addition of these substances to milk is forbidden 
by Federal and State laws. 

A simple test for preservatives may be made by 
setting a sample of milk aside and observing if it curdles 
within the usual time. If it does not, the presence of 
preservatives or alkalies may be suspected. The pre- 
servatives most conamonly used and tests for detecting 
their presence are given below. 

Boric Acid and Borax. — Until the introduction of for- 
maldehyde, boric acid and borax were the most popular 
preservatives; 0.1 to 0.2 per cent, of these substances will 
delay the curdling of milk for several days. They may be 
detected by the following tests : 

Villiers' and Fayolle's Test. — About 10 c.c. of the 
milk is placed in a porcelain crucible, evaporated to dry- 
ness and the residue burned to an ash. Sufficient sul- 

17 



258 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

phuric acid to make a paste is added to the ash and 3 
c.c. of methyl alcohol is mixed with it. The vapor which 
is then given off is ignited. If boric acid or borax is 
present, even in very small quantity, the flame will be 
green. 

Turmeric Test. — ^Add 6 or 7 drops of hydrochloric 
acid to 10 c.c. of milk and, after coagulation has occurred, 
filter. Dip a piece of turmeric paper into the filtrate and 
allow it to dry. If boric acid is present in the proportion 
of 0.02 per cent, or borax in the proportion of 0.03 per 
cent., the paper will be colored cherry-red (Kiihl) ; this 
color will be changed to bluish-black by ammonia water. 

Another method of applying the turmeric test is de- 
scribed by Farrington and WoU as follows : " One hun- 
dred cubic centimetres of milk are made alkaline with 
a soda or potash solution and then evaporated to dryness 
and incinerated. The ash is dissolved in water, to which 
a little hydrochloric acid has been added, and the solu- 
tion filtered. A strip of turmeric paper moistened with 
the filtrate will be colored reddish-brown when dried at 
100° C. on a watch glass if boric acid is present." 

Formaldehyde. — Formaldehyde, the favorite preserva- 
tive for milk, is used in the form of formaldehyde solution, 
formalin, formol, etc. A very small quantity (0.008 per 
cent, of formaldehyde, 0.02 per cent, of formalin) will 
prevent curdling for four days. The following tests may 
be used for detecting the presence of formaldehyde : 

Richmond's Test. — Place a small quantity of milk 
in a test tube, add an equal quantity of water and then 
pour a little commercial sulphuric acid slowly down the 
side of the tube so that it will form a layer at the bottom. 
A bluish or violet ring at the point where the acid and 
milk come in contact indicates the presence of formalde- 
hyde. If no formaldehyde is present a faint, greenish 



METHODS OF EXAMINING MILK 259 

ring is formed. This test will detect 1 part of formalde- 
hyde in 200,000 parts of milk. 

Leach's Test. — The reagent used in this test is a solu- 
tion of hydrochloric acid and ferric chloride consisting of 
998 c.c. of hydrochloric acid of a specific gravity of 1.2, 
and 2 c.c. of a 10 per cent, aqueous solution of ferric 
chloride. Place about 10 c.c. of milk and an equal quan- 
tity of this solution in a white cup or casserole and slowly 
heat over a flame to boiling, giving the fluid a rotary 
motion. If formaldehyde is present a blue or violet color 
appears. 

Salicylic Acid. — Salicylic acid is not often used to pre- 
serve milk because it is not very soluble in that fluid; 
0.04 per cent, will prevent milk from souring for 36 
hours. The presence of salicylic acid may be detected 
by the following test : 

Remonfs Test. — Place 20 c.c. of milk in a measuring 
cyhnder or large test tube, add 2 to 3 drops of sulphuric 
acid and 20 c.c. of ether. Mix by shaking and stand aside 
until the ether separates and forms a layer at the top. 
The fat of the milk and any salicylic acid present is 
dissolved by the ether. The ether solution is drawn off 
with a pipette, placed in a small crucible and evaporated 
by floating the crucible in hot water. The residue is 
rubbed up with a small quantity of 40 per cent, alcohol 
and filtered and a few drops of ferric chloride solution 
are added to the filtrate. A violet color appears if salicy- 
lic acid is present. 

Benzoic Acid. — Like salicylic acid, benzoic acid is also 
not very soluble, and consequently is not used very often 
to preserve milk. The various tests for this substance 
are all more or less complicated. 

Peter's test, as described by Leff mann, is as follows : 
" The material is made slightly acid and extracted with 



260 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

chloroform, which is then evaporated spontaneously. The 
vessel containing the residue is placed in melting ice, 2 c.c. 
of sulphuric acid added, and stirred until the residue is 
dissolved. Barium dioxide is dusted into the mass, with 
constant stirring, until the liquid begins to foam, when 
3 c.c. of hydrogen dioxide ( 3 per cent. ) are added drop 
by drop. The dish is then removed from the cold bath, 
the contents diluted with water to convenient bulk, and 
filtered. The acid filtrate is extracted with chloroform. 
The benzoic acid will have been converted into salicylic 
acid by the process and the latter may be detected by 
dilute solution of ferric chloride or ammonio-ferric sul- 
phate." 

Alkalies. — Alkalies delay the curdling of milk by 
neutralizing the acid formed by bacteria. The substances 
which have been used for this purpose are the carbonate 
and bicarbonate of soda, chalk, and potash. When mar- 
ket milk gives an alkaline reaction to litmus or has a low 
acidity, as determined by Mann's test, it should be tested 
for alkalies. This test is made as follows : 

Ten c.c. of milk are mixed in a test tube with an 
equal quantity of 95 per cent, alcohol, a few drops of a 
1 per cent, solution of rosolic acid are added and mixed 
with the other fluid by shaking. If an alkali is present 
the mixture will assume a rose-red color. If no alkali 
is present a brownish-yellow color will appear. 

STANDARD METHODS OF COUNTING BACTERIA ^ 

Collection of Samples. — The milk should be mixed 
thoroughly before the sample is taken and not less than 
10 c.c. should be collected for examination. Bottled 

^ From the report of the Laboratory Section of the Ameri- 
can Public Health Association, Oct. 24, 1916. 



METHODS OF EXAMINING MILK 261 

milk may be mixed by inverting the bottle several times. 
If the milk is in a vessel which is open and which can- 
not therefore be inverted, it may be stirred with the 
pipette which is used to transfer the sample to the sample 
bottle. The pipette should, of course, be sterile and 
should not be used to take another sample until it has 
again been sterilized. A sterile tube with straight sides 
should be used for taking a sample from a can. An 
aluminum tube i/4 inch in diameter and 21 inches long 
is most convenient. If the tube is held vertically, with 
the opening at the top unobstructed, and is inserted into 
the milk slowly until the lower end reaches the bottom of 
the can, it will contain a column of milk which will be 
representative of all the milk in the can. If the finger 
is then placed firmly upon the top of the tube, the column 
of milk can be withdrawn and transferred to a sterile 
sample bottle, which should be large enough to hold the 
entire contents of the tube, all of which must be emptied 
into the bottle. The tube must be washed and sterilized 
before being used to collect a sample from another con- 
tainer. If the temperature of the milk is to be taken, a 
separate sample should be used for this purpose and then 
discarded. Glass-stoppered bottles or those provided 
with cork-lined screw caps are the most satisfactory. The 
bottle containing the sample should be properly labelled 
and immediately placed in a carrying case containing 
cracked ice so that the milk will be promptly cooled to 
near the freezing point. The sample bottles should be 
transferred to the laboratory as soon as possible and the 
milk plated at once. If the plates are not prepared within 
four hours after the collection of the samples the elapsed 
time should be noted in the report. If the samples are 



262 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

placed in iced-water they may be kept for twelve hours 
without an increase in bacteria. 

All apparatus used for collecting, measuring, dilut- 
ing, and plating the samples must be sterilized by heat- 
ing at a temperature of at least 175° C. for one hour. 

There are two methods of counting bacteria in milk: 
The plate method, in which the number of bacteria per 
c.c. of milk is determined by counting the colonies de- 
veloping on agar plates to which a measured quantity 
of milk has been added; and the direct microscopic 
method, in which a small measured quantity of milk is 
spread over a definite area on a glass slide, dried, fixed 
and stained, and the bacteria counted under the micro- 
scope. The plate method is the oldest and best under- 
stood and is recommended for general purposes. The 
microscopic method is useful when rapid results are de- 
sired, as when samples are examined for the purpose of 
classifying or grading milk. 

PLATE METHOD 

Medium. — The medium used is standard beef extract 
agar, which should be prepared according to the follow- 
ing directions: 

" To 1000 c.c. of water add 5 grammes of peptone 
and 3 grammes of beef extract. The peptone shall be 
the best available, and the beef extract shall be Liebig's 
where this is obtainable. Weigh the containing dish and 
its contents. 

" Dissolve the peptone and beef extract by boiling 
and replace the water lost through evaporation. 

" While still hot filter through filter paper. 

" Add 12 grammes of oven-dried agar, or 15 grammes 
of market agar, and dissolve by boiling, or in an autoclav. 



METHODS OF EXAMINING MILK 263 

Kestore the weight lost by evaporation. It is imperative 
that the agar be of the best quality and clean, or it is 
impossible to obtain a clear medium. (When an auto- 
clav is at hand the following modification is convenient. 
Add the peptone and beef extract to about 300 c.c. of 
water, and the agar to 700 c.c. Heat both in an autoclav 
under 15 lbs. pressure one-quarter hour. Filter the broth 
while hot through filtered paper, and then mix the broth 
with the melted agar and filter through absorbent 
cotton. ) 

" Determine the acidity of the medium by titrating 
5 c.c, diluted with 45 c.c. water, with V20 normal NaOH, 
phenolphthalein being used as an indicator. Any at- 
tempt to adjust the acidity is likely to make undesirable 
changes in the medium. Inasmuch as variations between 
+.5 and +1. acid make no appreciable difference in the 
results, the reaction of the medium is not to be changed 
if it falls between + .5 and + -1 acid. It will usually be 
between these limits. If it should be above + 1. acid, add 
enough normal N'aOH to bring it to + 1., and if it is 
below + .5 acid add enough normal HCl to bring it to 
+ .5, always adding the smallest amount of the reagent 
possible to bring the reaction within these limits. 

" Cool to 45° C. and then heat to boiling ( 15 minutes) 
and filter through filter paper or absorbent cotton. It 
is necessary that the filtering be continued till the medium 
is clear. If the procedure here given is followed and a 
high grade of agar and other materials is used there will 
be no difficulty in getting the agar clear. Egg should 
not be used as a clarifier. 

*' After filtering, the agar may be either tubed, 10 
c.c. in each tube, or placed in flasks containing about 150 
c.c. each. The latter method requires less glassware and 



264 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

less time, and is found to be equally satisfactory for 
plating, as explained below. 

" Sterilize in an autoclav at 15 lbs. pressure (never 
above) for one-half hour after dry steam comes from the 
autoclav. As an alternative the medium may be steri- 
lized on three successive days in streaming steam, in 
which it must remain 20 minutes each day after the agar 
has completely melted. 

" If the flasks are to be kept for more than a couple 
of days, or are to be shipped, before using, cover the 
mouths of the flasks before sterilizing with paper fastened 
by a rubber band or by tinfoil to retard evaporation." 

Dilutions. — "For miscellaneous milk samples the 
character of which is not known three dilutions shall be 
made: 1-100, 1-1000, 1-10,000. Where the character 
of the milk is known the number of dilutions may be 
reduced. If the milk is pasteurized, certified, or 
known to be fresh and of high grade, the 10,000 
and 1000 dilutions may be omitted; if the milk is known 
to be old and of high bacterial content the 100 dilution 
may be omitted. In no case shall less than two plates 
be made of each sample. 

" Any convenient method of making dilutions may 
be used, always using pipettes and sterile water blanks. 
The water used for dilutions may be placed in dilution 
bottles (99 c.c. and 9 c.c. are convenient sizes) and 
sterilized for one hour in an autoclav at 15 lbs. pressure. 
These should be marked so that it can be determined that 
they have neither gained nor lost water during or subse- 
quent to sterilization. Or the water may be sterilized 
in bulk, if kept in a properly guarded container, and 
subsequently measured directly into dilution bottles with 
sterilized pipettes. 



METHODS OF EXAMINING MILK 265 

" The dilution bottles should have glass stoppers or 
some other type of closing that makes shaking possible. 
Cotton plugs are unsatisfactory because the dilution 
water will soak into the cotton. 

" Straight-sided pipettes graduated to deliver be- 
tween two marks are best, but pipettes marked to deliver 
may be used if care is taken that the points are not broken, 
and the tube is completely emptied. 

" In making dilutions the original sample and each 
dilution bottle shall be shaken 25 times, each shake being 
an up-and-down motion with an excursion of about one 
foot. After the final dilution fill a pipette to the mark 
and allow the contents to run into an empty Petri dish, 
the end of the pipette touching the bottom of the dish 
as the liquid runs out. If the pipette is one that delivers 
1 c.c, be sure that the last drop is carried into the Petri 
dish. (Pipettes should be placed immediately in water 
after using to make subsequent cleaning easier.) " 

Plating. — " The agar in the flasks (or test tubes) 
shall be melted in boiling water or steam and after 
melting should be cooled to 45° C. before using. 

" Pour 10 c.c. of the melted agar in each inoculated 
Petri dish, and by a gentle rotary motion thoroughly mix 
the agar and the diluted milk. As nearly as possible the 
same amount of agar should be poured into each Petri 
dish so that the depth of the agar in all be uniform. If 
desired, 10 c.c. may be measured out from the flask with 
a sterile pipette. 

" After dilution of the milk not more than half an 
hour should elapse before the agar is poured into the 
Petri dishes. 

" After the agar has thoroughly hardened place the 
Petri dishes in an incubating oven, inverted, in order to 



266 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

reduce the danger of spreaders. While clay tops of 
Petri dishes are useful for some purposes they are not 
recognized in the standard methods." 

Incubation. — " Only one period of incubation and 
one temperature is regarded as standard, 48 hours at 
37.5° C. In crowded incubators ventilation should be 
provided." 

Counting, — " If, among the different dilutions, there 
are plates containing from 30 to 300 colonies these should 
be counted, and the number, multiplied by the dilution, 
be reported as the final count. All colonies on such 
plates should be counted and the numbers averaged. If 
there are no plates within these limits the one that comes 
nearest to 300 is to be counted. No plate that contains 
less than twenty colonies shall be counted, unless it hap- 
pens that there are no plates with a larger number of 
colonies, or unless the numbers in the plates check with 
other dilutions. If the number of colonies on the plate 
to be counted is over 300, a part of the plate may be 
counted, and the whole plate averaged. 

" Counting shall be done with a lens, magnifying 
2Y2 diameters (or what the opticians call a 3^/^ + lens). 
Nearsighted persons should use their glasses in counting, 
but farsighted persons should remove them. In case it 
is doubtful whether certain objects are colonies or dirt 
specks they should be examined with a compound micro- 
scope." 

Reports. — " In making reports it must be borne in 
mind that with high numbers obtained by the routine 
method only an approximation to accuracy can be ob- 
tained. Only the left-hand figures of the final numbers 
are of significance. It is best, therefore, to report only 
the two left-hand figures of the results in order to avoid 



METHODS OF EXAMINING MILK 267 

an unwarranted impression of accuracy. For example, 
when the numbers are in millions no figures smaller than 
the millions have any significance in the routine analysis 
of milk. In making the report raise the number to the 
next highest round number, but never lower it. 

" In no case shall the count of a single plate be re- 
garded as sufficient for the purpose of grading milk. If 
a single sample of milk only is to be tested there should 
be at least three plates counted before a report is made." 

MICROSCOPIC METHOD 

The apparatus required for this method consists of 
a microscope, a supply of ordinary glass slides, and a 
straight capillary pipette marked to deliver 1/100 c.c, 
with the graduation mark 1% to 2% inches from the tip. 
The calibration should be tested by weighing on chemical 
balances the quantity of milk delivered when the pipette 
is filled to the mark. One pipette may be used for a num- 
ber of samples of milk provided it is kept clean. This 
may be done by rinsing the interior with clean water 
after each sample and wiping the exterior with a clean 
towel. 

Preparation of Smears. — " One one-hundredth c.c. 
of milk or cream is deposited upon a clean glass slide by 
means of the pipette above described. By the use of a 
clean stiif needle this drop of milk is spread over an 
area of one square centimetre. This may be most con- 
veniently done by placing the slide upon any glass or 
paper ruled into areas one centimetre square. These 
marks showing through the glass serve as guides. After 
uniform spreading the preparation is dried in a warm 
place upon a level surface. In order to prevent notice- 
able growth this drying must be accomplished within 



268 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

five to ten minutes ; but excessive heat must be avoided 
or the dry fihns may crack and peel from the slides in later 
handling. 

" After drying the slides are to be dipped in xylol 
(gasoline may be used) for one minute, then drained 
and the slides dried. They are then immersed in 90 per 
cent, grain or denatured alcohol for one minute or more 
and then transferred to a fresh aqueous solution of methy- 
lene blue. Old or unfiltered stains are to be avoided, as 
they may contain troublesome precipitates. The slides 
remain in this solution from five seconds to one minute 
or longer, depending upon the effect desired, and are then 
rinsed in water to remove the surplus stain, and decolor- 
ized in alcohol. The decolorization takes several seconds 
to a minute, during which time the slides must be under 
observation in order that the decolorization may not pro- 
ceed too far before they are removed from the alcohol. 
When properly decolorized the general background of 
the film should show a faint blue tint. Poorly stained 
slides may be decolorized and restained as many times as 
necessary without any apparent injury. After drying, 
the slides may be examined at once, or they may be filed 
away and preserved for further reference." 

Standardization of the Microscope. — " The micro- 
scope to be used must be adjusted in such a way that 
each field of the microscope covers a certain known frac- 
tion of the total square centimetre's area. This pro- 
cedure is simple with the proper materials at hand. The 
microscope should have a 1.9 mm. (V12 inch) oil immer- 
sion objective, and an ocular giving approximately the 
field desired, and should preferably be fitted with a 
mechanical stage. To standardize the microscope, place 
upon the stage a stage micrometer, and by the selection 



METHODS OF EXAMINING MILK 269 

of oculars or adjusting the draw tube, or both, bring the 
diameter of the whole microscopic field to .205 mm. 
When so adjusted the microscopic field will cover almost 
exactly 1/300,000 of a cubic centimetre of the milk 
(actually 1/302840). This means that if the bacteria 
in one field only are counted the number should be 
multiplied by 300,000 to give the total number in a cubic 
centimetre. If the bacteria in a hundred fields are to 
be counted the total should of course be multiplied by 
3000. 

" Inasmuch as it is difficult to count bacteria lying 
near the margin of the microscopic field, it is much better 
to have an eyepiece micrometer with a circular ruling 
8 mm. in diameter and divided into quadrants. This 
will give, in the microscopic field, a smaller area within 
which the bacteria may be seen most sharply, and which 
may be more easily counted. Such eyepiece micrometers 
are now manufactured by laboratory supply houses and 
may be easily obtained. In the use of this eyepiece 
micrometer the inner circle, by the adjustment of the 
draw tube, should be made to cover a circle with a diam- 
eter of .146 mm. In this case this inner circle will cover 
1/600,000 of a cubic centimetre of milk, meaning, of 
course, that the number of bacteria in a single field should 
be multiplied by 600,000, or, if a hundred fields are 
counted, by 6000, to obtain the number per cubic centi- 
metre. 

" The number of microscopic fields to be counted will 
depend somewhat upon the kind of data that is desired. 
If this method is to be used simply for the purpose of 
dividing milk into grades, it will in most cases be un- 
necessary to do the actual counting, since a Grade A 
milk will show field after field without any bacteria at 



270 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

all, while a Grade C milk will show the field crowded with 
bacteria. In all doubtful cases, however, counting should 
be done, and there should never be less than thirty fields 
counted in order to have reliable results. Counting thirty 
fields is not so tedious a task as it would seem to be, since 
in ordinary milk the number of bacteria in each field is 
small, and the counting may be done very rapidly." 

Counting. — ■*' Counting the bacteria in such a smear 
may be done in two ways: 1. The number of groups of 
one or more bacteria present. 2. The number of indi- 
viduals. The second, of course, is really the correct count 
of the number of bacteria, but the former will give a 
count much closer to that obtained by the plate count, 
since the colonies upon the plate represent groups of bac- 
teria rather than individuals, each group growing into 
a single colony only. Extensive tests have shown that 
there is a fair correspondence between the number of 
groups reported by experienced obsei^ers and the num- 
ber of colonies that may grow in plates made from the 
same milk, although there are occasionally discrepancies 
of considerable extent. These discrepancies are caused 
by variations in judgment as to what constitutes a 
group, variations in the extent to which gi'oups break 
up in the dilution waters when the smears are made, 
and the presence of dead bacteria or of bacteria which do 
not grow on the plates. Some experience is needed by 
the microscopist in determining just what should be 
counted. In high-grade milks an inexperienced person 
is apt to fail to recognize differences between bacteria 
and other minute objects. This results as a rule in an 
overcount by inexperienced men. In milk containing 
many readily recognizable bacteria in each field the in- 



METHODS OF EXAMINING MILK 271 

experienced man is apt to overlook some of them, giving 
an undercomit. These difficulties are overcome, how- 
ever, by training and experience. 

COMPARISON OF RESULTS OBTAINED BY THE TWO METHODS 

" It must be recognized that the results obtained from 
the microscopic record give a closer approximation to 
the actual number of bacteria present in the milk than 
those obtained by the plate method, since the plate 
method will count as one either a single bacterium or a 
group which may sometimes contain a hundred or even 
more individuals. Inasmuch, however, as the plate count 
has become a method of analysis that is well known and 
commonly applied, it becomes desirable to know as closely 
as possible what relations there may be between the plate 
count and the microscopic count. Experience has shown 
that the count of individual bacteria is ordinarily 1.5 to 8 
times as great as the plate count, the ratio between the 
two being largely dependent upon the size of the clumps 
of bacteria present. Where the bacteria are mostly iso- 
lated, the ratio of the two counts would be much closer 
than where there are present long chains of streptococci 
or masses of cocci. After one has had a little experience 
in counting clumps it is found that the number of groups 
shown by the microscope agrees fairly well with the num- 
ber of colonies shown by the plate count, though even here 
there are occasionally discrepancies, due among other 
things to the appearance in the microscope of kinds of 
bacteria which fail to grow in the culture media used in 
making plates. In all cases, however, the direct count of 
raw milk will give a much closer approximation to the 
actual numbers of bacteria than the plate count. In view 
of these facts it is difficult to interpret one count in terms 



272 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

of the other ; but a few suggestions will give a fairly sat- 
isfactory idea as to how the two may be related. 

"Grade A raw milk, which should have less than 100,- 
000 bacteria per c.c, will not show more than three to four 
small clumps of bacteria for each 30 fields of the micro- 
scope where the diameter of the fields is .205 mm. Such 
milk also ought not to contain more than 500,000 individ- 
ual bacteria per c.c. when counted by the microscope. 
For Grade A pasteurized milk (which should have less 
than 200,000 per c.c. by the plate count before pasteuri- 
zation) the microscope should not show more than six to 
eight clumps per 30 microscopic fields, and not more than 
1,000,000 individual bacteria when counted with the 
microscope. 

"Grade B milk, which is supposed not to have more 
than 1,000,000 bacteria before pasteurization, when 
counted by the plating method, should not show more 
than 20 individual bacteria per field, where the diameter 
of the fields is .205 mm., and not more than three to four 
groups of bacteria per field. 

""While the above relation between the plate count 
and the microscopic counts cannot be relied upon as hav- 
ing a very great amount of accuracy, it will serve to give 
a general idea of the ratio between the two under or- 
dinary conditions, and may serve as a guide in the use of 
the direct microscopic method." 

EXAMINATION FOR STREPTOCOCCI 

When long-chain streptococci are found in milk sedi- 
ment in association with an excess of leucocytes and the 
latter cells are clumped together and consist largely of 
the polymorphonuclear type, there need be no hesitancy 
in concluding that the streptococci are pathogenic and 



METHODS OF EXAMINING MILK 273 

that the milk under examination contains the secretion of 
a cow affected with catarrhal mastitis. 

If the plates prepared from a sample of herd milk 
contain a large nmnber of extremely minute brownish 
colonies, which upon microscopic examination are found 
to consist of streptococci in rather long chains, an ex- 
amination of the herd from which the milk came will re- 
sult in the discovery of one or more cows affected with 
catarrhal mastitis. To examine microscopically, place one 
of the colonies in a drop of water on a glass slide and 
spread by a gentle rotary motion of the platinum nee- 
dle, beginning at the centre and working outward ; dry, 
fix by heat and stain with methylene blue. The chains 
of Streptococcus lacticus are shorter than those of the 
streptococci of mastitis, rarely containing more than 6 or 
8 cocci, and the individual cocci are arranged as diplo- 
cocci. (See Figs. 5 and 6.) 

The method of examination for streptococci recom- 
mended by the Laboratory Section of the American 
Public Health Association is as follows : 

" Where streptococci, diplococci, or cocci are found in 
the sediment, and the plate from the same sample con- 
tains colonies resembling streptococci colonies, these colo- 
nies may be grown in bouillon to see if chains will develop. 

"First make and record an estimate of the number of 
such colonies present, then transfer from 10 to 50 of them 
to bouillon and grow for 15 to 24 hours at 37° C. To ex- 
amine the bouillon culture, spread a loopful on a glass 
slide, fix with heat, fix with alcohol while slide is still quite 
hot, stain with methylene blue, wash inmiediately, dry 
and examine. 

"A milk should not be condemned because a few 
chains are found together with large numbers of other 
18 



274 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

microscopic organisms in a bouillon culture, but it is safer 
to exclude a milk from the market when these three tests 
agree : 

"1. Microscopic examination of the sediment shows 
streptococci, diplococci, or cocci. 

"2. The plate from the same sample shows colonies 
resembling streptococci colonies exceeding a count of 
100,000 to a cubic centimetre. 

"3. The bouillon culture from these colonies shows 
long-chain streptococci alone or in great excess compared 
with the other bacteria present. 

"Milk showing in the stained sediment both abund- 
ance of long-chain streptococci and pus should be con- 
demned as unsafe." 

The bouillon used in this examination may be pre- 
pared as follows : 

"Infuse 500 g. finely chopped lean meat 24< hours 
with 1,000 c.c. distilled water in refrigerator; restore loss 
by evaporation; strain infusion through cotton flannel." 
(Or, dissolve 5 g. of beef extract, preferably Liebig's, 
in 1,000 c.c. distilled water.) 

" Add 1 per cent, peptone. Warm on water bath, 
stirring until peptone is dissolved. 

" Heat over boiling water or steam bath thirty min- 
utes. Restore loss by evaporation. 

"Titrate, adjust reaction to + 1 per cent, by adding 
normal sodium hydrate. 

"Boil two minutes over a free flame, constantly stir- 
ring. Restore loss by evaporation. 

"Filter through absorbent cotton, passing the liquid 
through until clear. Titrate and record final reaction. 
Tube, using 10 c.c. to each tube. Sterilize." 



METHODS OF EXAMINING MILK 275 

EXAMINATION FOR COLI 

The presumptive tests for Bacillus coli do not have 
the same value in milk examination as in water analysis, 
because it is practically impossible to obtain milk from 
the cow, even under good dairy conditions, without it 
being infected to some extent with colon bacilli from the 
intestines of the animal. The detection of this organism 
in milk is therefore of little value, except that when it is 
present in large numbers it is an evidence of uncleanli- 
ness and usually an indication of gross fecal contamina- 
tion. 

One of the presumptive tests for Bacillus coli in milk 
approved by the Laboratory Section of the American 
Public Health Association is made as follows : "1 c.c. of 
a 1 to 1,000 dilution of milk is placed in ordinary bile 
containing 1 per cent, lactose in a fermentation tube and 
allowed to stand at 37° C. for 72 hours, at the end of 
which time, if there is more than 15 per cent, gas, plates 
are made, colonies isolated and run through species tests." 

The fermentation test described on page 278 is a 
simple and convenient method of detecting the presence 
of an excessive number of coli or other gas-forming or- 
ganisms in milk. 

EXAMINATION FOR TUBERCLE BACILLI 

The method recommended by the Laboratory Section 
of the American Public Health Association is as follows : 

"Pint or quart samples of milk should be obtained, 
kept well iced, and delivered to the laboratory as soon as 
possible. The milk and cream should be well mixed by 
shaking vigorously. 50 c.c. of the mixed milk are then 
transferred to a large centrifuge flask and 100 c.c. of 
sterile water added. Centrifuge for one hour at 2,000 



276 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

revolutions per minute. The milk is diluted with twice 
its volume of water with the idea that it will decrease the 
specific gravity of the milk and so permit of the easier 
sedimentation of the tubercle bacilli. Guinea pigs are 
then inoculated, subcutaneously in the belly wall, with 5 
c.c. of the sediment thus obtained. The guinea pigs not 
dying in at least two months are chloroformed, after 
being tested with tuberculin, and careful autopsies made. 
Smears, cultures and sections are made from the various 
organs of the animals that show any change from the nor- 
mal. The smears are stained with carbol f uchsin and ex- 
amined for acid-fast bacilli. 

" Cultures are made on glycerinized potato and glyc- 
erine agar to rule out Rabinowitch's quick growing acid- 
fast butter bacillus. 

"Sections are stained with carbol f uchsin for tubercle 
bacilli and also with heematin and eosin for histological 
appearances. 

"Tuberculous guinea pigs may be differentiated from 
nontuberculous by giving sufficient crude tuberculin (2 
c.c. ) subcutaneously to cause the death of the tuberculous 
animals in twenty- four hours. 

"It is of course understood that the examination of 
milk for tubercle bacilli is by the very natm-e of the test 
limited. For the control of this disease in cattle we must 
rely upon the tuberculin test." 

MicroscopicMethod — Some of the sediment obtained by 
centrifugalizing the milk is spread thinly on a glass slide, 
fixed by heating, stained with carbol fuchsin, decolorized 
in acid alcohol and counter-stained with methylene blue. 
If small flakes or clots are present in the milk, one of 
these is spread on the slide and treated in the same man- 
ner. The carbol-fuchsin solution is prepared by dissolv- 



METHODS OF EXAMINING MILK 277 

ing 1 gramme of fuchsin in 10 c.c. of alcohol and 100 c.c. 
of a 5 per cent, solution of phenol in water, and then 
filtering the solution. The acid alcohol is prepared by- 
mixing 5 CO. of nitric or one of the other mineral acids 
with 95 c.c. of alcohol. After the smear on the slide has 
been fixed, it is flooded with carbol fuchsin and the slide 
is held over a Bimsen flame and the stain kept steaming 
for 3 minutes. The slide is then rinsed with water and 
the preparation treated with the acid alcohol until the 
red color disappears. Next, the acid alcohol is rinsed off 
with water and the preparation is stained for 3 minutes 
with methylene blue, after which the slide is washed with 
water, dried, and examined with the 1/12 oil immersion 
objective. Any tubercle bacilli present will be stained 
red; other organisms will be stained blue. While the 
presence of tubercle bacilli may be accepted as proof that 
the cow from which the milk came is infected with tuber- 
culosis, failure to find these organisms cannot be re- 
garded as positive evidence that the animal is not tuber- 
culous. Tubercle bacilli may be present in small numbers 
and escape detection on microscopic examination. The 
so-called acid-fast organisms are also stained red by car- 
bol fuchsin. They may be present in milk and butter, but, 
apparently, they usually enter the milk after it is drawn 
from the udder. Jensen is of the opinion that if precau- 
tions are taken to prevent contamination of the milk 
sample when it is drawn from the udder, these organisms 
will very rarely cause errors in diagnosis. 

Antiformin Method. — Take 5 c.c. of the milk to be ex- 
amined and mix it with 5 c.c. of absolute alcohol, 5 c.c. 
of ether, 10 c.c. of a 25 per cent, solution of antiformin 
and 25 c.c. of normal saline solution. Place in an incu- 



278 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

bator for at least one-half hour. Centrifugalize, prepare 
a slide from the sediment, and stain as described for the 
microscopic method. 

FERMENTATION TEST 

The fermentation test has been in use in cheese fac- 
tories for a long time to detect milk which is unsuitable 
for cheese-making. It can be used in milk control work 
to discover the presence of the more objectionable milk 
bacteria, such as the gas-formers and peptonizers, and 
thus ascertain what form of decomposition the milk is 
likely to undergo with age, especially if improperly cared 
for. It is also of assistance in determining the source of 
excessive bacterial contamination. 

The test is very simple and does not require any spe- 
cial apparatus. In cheese factories, bottles holding from 
120 to 140 c.c. or test tubes of 40 to 50 c.c. capacity are 
used for the milk samples. After the milk is introduced, 
they are closed with a rubber stopper and are held at a 
temperature of 37 to 38° C. in a water bath. In a labora- 
tory, it is more convenient to use the test tubes ordinarily 
used for bacteriological cultures and to place the tubes 
in an incubator after the milk has been placed in them. 

The test tubes are washed and cleansed in the usual 
manner, plugged with cotton and sterilized by heating in 
a hot-air sterilizer for 2^/^ hours at 150 to 160° C. It is 
important that the tubes be sterilized, since any organ- 
isms in the tubes will develop in the milk and may influ- 
ence the result. Each tube is numbered with a paraffine 
pencil to correspond with the sample of milk and is then 
filled with milk to within a finger's breadth of the bottom 
of the cotton plug, closed with the cotton plug and placed 
in the incubator. In transferring the milk from the ves- 



METHODS OF EXAMINING MILK 279 

sel in which it was collected to the test tube, the necessary 
precautions should be observed to prevent contamination. 

Twelve hours after they are placed in the incubator, 
the samples are examined. If the milk is normal, fresh 
and of good quality, there will be no change apparent ex- 
cept perhaps a clean, sour odor. The beginning of fer- 
mentation or curdhng is indicated by an upward bulging 
of the cream layer and the presence of a greenish layer 
beneath it. If there is no change at this time, the samples 
are to be replaced in the incubator and observed again in 
twelve hours, and subsequently at twelve-hour periods if 
necessary. If curdling does not take place after forty- 
eight hours, the reaction of the milk should be taken and 
tests made for preservatives. When the milk curdles, the 
time of curdling and the character of the curd are to be 
noted. The time of curdling depends upon the number of 
bacteria present which are not inert, while the character 
of the curd depends upon the kind of bacteria which pre- 
dominate. The types of curds, the symbols by which they 
are recorded, and their indications are as follows : 

1. Jelly-like Curd. — Ji, solid, smooth, white, jelly- 
like curd, with no fluid. J2, curd of same type, but show- 
ing a few furrows or gas bubbles. J3, curd same, but 
showing more fuiTows and gas bubbles and also cracks, 
with some fluid. The jelly-like curd is produced when 
the acid-forming bacteria predominate, and if the number 
of bacteria is excessive it usually indicates that the milk 
vessels or utensils are unclean, or that the milk is old or 
has not been kept under proper conditions. 

2. Peptonized Curd. — The curd may be firm, jelly- 
like, with ragged surfaces, or it may be soft, flocculent 
or "mushy," associated in either case with more or less 
fluid. Pi, the amount of fluid is small in proportion to 



280 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

the size of the curd. P2, increased amount of fluid, less 
curd. P3, amount of fluid large in proportion to the size 
of the curd. This type of curd is produced when a large 
proportion of peptonizing bacteria are present in the 
milk. When the number of bacteria is large, it is usually 
an indication that the milk has been contaminated with 
dust from hay, fodder or soil, or that a suppurative con- 
dition is present in the herd. When milk is produced 
under good conditions and is kept cool, the peptonizing 
bacteria (udder cocci) will predominate but the total 
number of bacteria will be small. 

3. Gaseous Curd. — A white, jelly-like curd contain- 
ing gas bubbles and, when gas has been formed in large 
quantity, presenting a sponge-like appearance. More 
or less fluid is present and this may also contain gas bub- 
bles. Gi, a few gas bubbles in the cream layer or in the 
curd. G2, gas bubbles numerous in the cream and curd ; 
gas bubbles may also be present in the fluid. G3, curd 
sponge-like, containing many gas bubbles ; may be split 
and a portion driven to the top; gas bubbles in fluid. 
The gaseous curd is produced when a large percentage 
of gas-forming bacteria is present and is usually an in- 
dication that the milk has been contaminated with an ex- 
cessive amount of manure. It may also occur when pol- 
luted water is used to wash the milk vessels and utensils. 

4. ''Flaky" or Flocculent Curd. — Curd in flakes or 
flocculi, associated with a turbid fluid, which may be 
whitish, yellowish, or otherwise discolored. Fli, curd in 
fine flakes or partially homogeneous. FI2, large flakes 
and considerable fluid. Fla, large flakes, torn, with white 
or discolored fluid. This type of curd is produced when 
saccharomyces which ferment lactose are present in large 
numbers. The casein is permeated with fine gas bubbles 



METHODS OF EXAMINING MILK 281 

at the moment of precipitation, which causes it to be 
broken up into flakes ; the fluid is turbid because of the 
movement produced by the gas developed (O. Jensen). 

ESTIMATION OF THE NUMBER OF LEUCOCYTES 

There are a number of methods for determining the 
leucocyte content of milk, each having a different limit 
for normal milk. In several, the milk is centrifugalized, 
a portion of the sediment is spread on a glass slide, fixed, 
and stained, and the number of leucocytes in the field of 
the 1/12 oil immersion objective is counted. In others, 
the leucocytes in a measured volume of sediment or milk 
are counted or the quantity of sediment in a definite vol- 
ume of milk is measured. Of these methods, those most 
commonly used are the following : 

Stokes' Test. — 10 c.c. of milk is placed in a sediment 
tube and centrifugalized for 10 minutes, after which the 
cream and separated milk are poured ofl*. A platinum 
loopful of the sediment is spread on a glass slide over an 
area of 1 square centimetre, dried in the air, fixed in the 
flame, and stained with methylene blue for 2 or 3 minutes. 
The specimen is then placed under the microscope and 
examined with the 1/12 oil immersion objective. The 
number of cells in the field of vision are counted. The 
leucocytes in 10 fields in different parts of the prepara- 
tion are counted and the average per field determined. 
The limit for normal milk is 10 leucocytes to the field. 

Stewarfs Test. — Special tubes, closed with a rubber 
stopper at the bottom, are used for this test, and a spe- 
cial centrifuge head is also required. One c.c. of milk is 
placed in the tube and centrifugalized for ten minutes. 
This throws the sediment down on the upper surface of 
the rubber stopper at the bottom of the tube. The stop- 



282 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

per is removed, and the sediment spread on a glass slide 
by rubbing the stopper over an area of 1 square centi- 
metre. The preparation is dried in the air, stained 2 
minutes with Jenner's blood stain and examined under 
the microscope with the 1/12 oil-immersion objective and 
a No. 3 ocular. The leucocytes in 10 fields are counted. 
An average of 23 cells to the field is the limit for normal 
milk. If the average number of cells to the field is mul- 
tiplied by 4400 the approximate number of cells per c.c. 
is obtained. 

Doane-Buchley Method. — 10 c.c. of milk is centrifu- 
galized for 10 minutes in a graduated sediment tube, after 
which the cream and separated milk is drawn off with a 
pipette down to the 1 c.c. mark. A drop of saturated al- 
coholic solution of methylene blue is mixed with the re- 
maining portion and the mixture is allowed to stand one 
minute to stain the cells. One drop of this mixture is 
placed in a Thoma-Zeiss blood-counting apparatus and 
the number of leucocytes per c.c. determined. The limit 
for normal milk is 500,000 per c.c. 

Trommsdorff Test. — For this test a special sediment 
tube is used which is drawn out at the lower end into a 
small capillary tube with twenty graduations, each grad- 
uation representing 0.01 per cent. 10 c.c. of milk is 
placed in the tube and centrifugalized for 10 minutes. 
The volume and color of the sediment in the capillary 
tube are then noted. The limit for sediment in milk from 
individual cows in normal condition is 0.1 per cent, and 
the color should be white or grayish white. If the sedi- 
ment exceeds this amount and is of a yellowish-color, the 
presence of mastitis secretion is indicated and the sedi- 
ment should then be examined microscopically to deter- 
mine whether it consists largely of leucocytes or of debris 



METHODS OF EXAMINING MILK 



283 



I 



and if streptococci are present. In fresh cows, the sedi- 
ment is usually of a grayish- white or white color and or- 
dinarily does not exceed 0.08 per cent; sometimes the 
sediment is red, which is an indication of the presence of 
red blood cells. 

In all of these tests the kind of leucocytes should re- 
ceive attention as well as the number. 
A preponderance of polymorphonu- 
clear leucocytes is very significant, 
since in mastitis three-fourths and 
more of the eells are of this type. The 
clumping or grouping of the cells is 
also characteristic of milk containing 
mastitis secretion. There is an in- 
creased number of epithelial cells in 
the milk of cows affected with mas- 
titis; in catarrh of the milk cistern, 
nests of elongated epithelial cells may 
be observed in the sediment. 

When an excessive number of leu- 
cocytes is found in market milk, with 
a preponderance of polymorphonu- 
clear cells showing the characteristic 
clumping or grouping, an examination 
of the herd from which the milk came 
will usually disclose the presence of 
mastitis or other suppurative condition. In such cases, 
however, it must be remembered that leucocytes are in- 
creased in number in the milk at the beginning and near 
the end of lactation and following incomplete or delayed 
milking. Heating milk to 60° C. (140° F.) or above 
also increases the number of leucocytes in the sediment. 
When the number of leucocytes in market milk falls 



Fig. 39. — Sediment tube 
used in the Trommsdorff 
test, Bhowing graduations 
in the capillary extension 
at the bottom. 



284 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

within the linoits set for normal milk, the possible pres- 
ence of mastitis secretion is not excluded. 

The presence of numerous streptococci in connection 
with an excess of leucocytes is strong evidence that the 
milk contains secretion from an inflamed udder. Milk 
may contain non-pathogenic (Streptococcus lactictis) as 
well as pathogenic streptococci but, as was first pointed 
out by Bergy, the streptococci may be regarded as path- 
ogenic when they ai e associated with a large number of 
polymorphonuclear leucocytes, especially if they are in 
long chains. The presence of cocci, diplococci, or short 
chains within the cells is also significant. Furthermore, 
the pathogenic streptococci usually form longer chains 
than the non-pathogenic, chains of Streptococcus lacticus 
rarely containing more than 6 or 8 organisms. (See 
Figs. 5 and 6) . According to Ernst, the mastitis strep- 
tococci can be recognized by the shape of the individual 
cocci and the leBgth of the chain. ( See page 53. ) 

The leucocyte tests are more reliable for individual 
milk than for market milk. In comparisons of the leuco- 
cyte tests with the catalase test in the examination of in- 
dividual milk to discover evidence of mastitis, the catalase 
test has proven the more accurate. 

BOILING TEST 

A small quantity of milk is placed in a vessel and 
boiled, after which it is examined for flakes or curds. In 
the laboratory, about 10 to 15 c.c. of milk is placed in a 
test tube, which is then held over a Bunsen flame until the 
milk boils. Fresh, normal market milk will not curdle. 
When curdling occurs, it indicates that the milk has un- 
dergone excessive acid fermentation, either because it is 
stale, or was produced under unclean conditions, or was 



METHODS OF EXAMINING MILK 285 

not properly cooled and cared for. When tested in this 
manner, milk will curdle before a sour taste is apparent 
and several hours before it will curdle spontaneously. If 
boric acid has been added to the milk as a preservative 
this will increase the acidity and influence the test. Sali- 
cylic acid generally has no influence because it is not usu- 
ally added in sufficient quantity. 

Milk also cm^dles when boiled when there is an excess 
of albumin or globulin present. In normal milk, albumin 
and globulin are not present in sufficient amount to make 
curdling visible when the milk is boiled. The udder se- 
cretion from individual cows will curdle on boiling for 
two to four days after parturition. Boiling will also cur- 
dle milk from cows affected with inflammation of the 
udder, cowpox, and nymphomania. During oestrum the 
milk sometimes curdles when boiled. It is necessary to 
test the milk of the individual cow to obtain a positive 
reaction in these cases. If the milk from the affected cow 
is mixed with the milk from other cows in the herd, the 
albumin or globulin may be so diluted that curdling will 
not be apparent. 

ALCOHOL TEST 

In applying the alcohol test, exactly equal quantities 
by volume of milk and 68 per cent, alcohol are mixed to- 
gether, after which the mixture is examined for flakes or 
curds. The flakes may be quite small and must be looked 
for carefully. The test is most conveniently made with 
a test tube marked for 5 c.c. and 10 c.c. The tube is filled 
to the 5 c.c. mark with 68 per cent, alcohol, and to the 10 
c.c. mark with milk, and the two fluids are then mixed 
by shaking. Milk should not be tested when cold, be- 
cause at low temperatures casein has a tendency to clump 
and form flakes. The flakes of fat formed when milk is 



286 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

agitated must not be mistaken for cm-ds or flakes result- 
ing from the alcohol reaction. 

The 68 per cent, alcohol is made by mixing 68 parts of 
absolute alcohol with 32 parts of distilled water. The 
alcohol should be neutral. This can be determined by 
adding a few drops of phenolphthalein solution to a small 
quantity of the alcohol and then running in a drop of 
tenth-normal sodium hydroxide solution. If the alcohol 
is neutral the mixture will assume a permanent pink 
color. 

Fresh normal market milk will not curdle when 
tested in this manner. Milk which has undergone acid 
fermentation, or which has been acted upon by the rennet- 
like ferment produced by certain species of bacteria, or 
which has undergone a combined acid and rennet fermen- 
tation, will curdle when these processes have operated to 
a certain extent. A positive reaction therefore results 
when the milk has undergone a certain degree of bacterial 
decomposition and is an indication that the milk is old, or 
that it was produced under unclean conditions, or that it 
was not properly cooled and cared for. 

The milk of individual cows will give a positive reac- 
tion for from four to twelve days after parturition and 
near the end of lactation. For a rather long time after 
abortion, the milk will also give a positive reaction. Milk 
from cows with diseased udders will react positively be- 
fore any clinical symptoms are apparent and also for a 
time after the disease has clinically healed. Milk from 
cows affected with diseases or injuries of the genital tract, 
diseases of the digestive tract, or advanced tuberculosis 
will also usually give a positive reaction to the alcohol 
test, but not always. It appears that a positive reaction 
occurs in these cases only when pathological products are 



METHODS OF EXAMINING MILK 287 

absorbed from the diseased area and eliminated, in part 
at least, through the udder. While a negative reaction 
may not always indicate the entire absence of disease, the 
presence of any diseased condition which affects the 
udder directly or indirectly is indicated by a positive re- 
action, excluding, of course, cows which are "fresh," near 
the end of lactation, in heat, or which have recently 
aborted. 

The alcohol test is a more delicate test for bacterial 
decomposition and for the presence of inflammatory and 
other pathological products than the boiling test and will 
give a positive reaction when the boiling test is negative. 

CATALASE TEST 

The amount of catalase in milk is measured by the 
amount of oxygen which is separated when a measured 
quantity of hydrogen peroxide is added to a certain quan- 
tity of milk. Different forms of apparatus are used for 
collecting and measuring the oxygen, the one most com- 
monly used being the Gerber-Lobeck apparatus. 

The quantity of oxygen separated will depend not 
only on the amount of catalase in the milk, but also upon 
the amount of hydrogen peroxide added. The quantity 
of oxygen separated increases with the amount of hydro- 
gen peroxide added up to a certain point, but if hy- 
drogen peroxide is present in excess of this amount it 
will exert a depressing effect upon the ferment. For 
this reason it is necessary to standardize the hydrogen 
peroxide solution used, and since the solution is unstable 
it must be standardized from time to time. 

A 1 per cent, solution of hydrogen peroxide is used 
in the test. The ordinary preparations of hydrogen per- 
oxide are 3 per cent, solutions and must therefore be 



288 



PRINCIPLES AND PRACTICE OF MILK HYGIENE 



—3 



9_a 



tei<:-* 



diluted with twice the quantity of 
water to prepare a 1 per cent, solu- 
tion. Distilled water or well-boiled 
and filtered water should be used. 
For example: 100 c.c. hydrogen per- 
oxide, 200 c.c. distilled water. The 
solution should be standardized by 
titration with a tenth-normal potas- 
sium permanganate solution, as 
follows : 

Ten c.c. of the hydrogen peroxide 
solution is mixed with 90 c.c. of dis- 
tilled or boiled water. Of this solu- 
tion, 10 c.c. is placed in a beaker 
with 10 c.c. of dilute sulphuric acid. 
The dilute sulphuric acid is prepared 
by adding 400 c.c. of distilled water 
to 100 c.c. of sulphuric acid with a 
specific gravity of 1.82 to 1.825. 
About 5 c.c. of the tenth-normal solu- 
tion of potassium permanganate is run 
into the beaker from a burette and it 
is then added slowly until the solution 
takes on a pale violet color which 
remains after stirring. About 6 c.c. 
will be required for a 1 per cent, solu- 
tion of hydrogen peroxide. Each 
c.c. of the tenth-normal potassium 

c.c. mark and elevated it a , i i • • i j_ 

corresponding degree in the pcrmaugauate solutiou IS cqual to 

outer tube. (Courtesy Cor- . _ 

neii Veterinarian.) 0.0017008 gram hydrogcu peroxide. 

Example: 0.0017008 X 6 p= 0.0102048 X lOQ = 1.02 
per cent, hydrogen peroxide. 

The hydrogen peroxide solution should be kept in an 






FiQ. 40. — Gerber-Lobeck 

catalase apparatus. 1. Bottle 
with perforation in neck at a. 
2. Volumeter, showing (a) the 
middle tube, with scale; (6) 
the inner tube, through which 
the oxygen ascends from the 
bottle to the top of the middle 
tube, and (c) the openings 
through which the water es- 
capes from the middle to the 
outer tube. In the illustra- 
tion, oxygen collected at the 
top of the middle tube has 
depressed the water to the 3 



METHODS OF EXAMINING MILK 289 

amber colored bottle, well stoppered and in a cool place. 
High temperatures break up the compound. The bottle 
should be closed immediately after being opened to draw 
off any of the solution. The solution must be tested by 
titration from time to time in order to insure accurate re- 
sults. 

To overcome the inconvenience of frequent tests of 
the hydrogen peroxide solution, the N. Gerber Co., of 
Leipsig, Germany, has prepared a tablet containing the 
hydrogen peroxide in more stable form. One of these 
tablets dissolved in 5 c.c. of water makes a 1 per cent, 
solution of hydrogen peroxide. ( It has also been estab- 
lished by extensive experiments that one of these tablets 
added to 10 c.c. of milk will give the same result as 3 c.c. 
of a 1 per cent, hydrogen peroxide solution in 9 c.c. of 
milk). 

The test is made as follows: 1. The bottles must 
be well cleaned and sterilized by boiling for 15 minutes 
before using. The use of water containing calcium must 
be avoided. If not used at once the bottles are to be 
tightly corked with rubber stoppers, which are also to 
be sterilized by boiling. The bottles may be closed with 
cotton plugs and sterilized in a hot-air sterilizer. Pipettes 
should be sterilized before beginning a series of tests. 
The pipette used for measuring the milk should be 
washed out with cold water and then sterilized by filhng 
it with boiling water after each sample of milk is meas- 
ured. 

2. Three c.c. of a 1 per cent, solution of hydrogen 
peroxide is placed in the bottle ; then 9 c.c. of the milk to 
be tested is added. The bottle is numbered to correspond 
with the sample of milk. In testing individual milk, it 
is recommended that the sample be taken from the entire 

19 



290 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

quantity of milk obtained at a milking, or from the total 
quantity obtained from each quarter, if it is desired to test 
each quarter separately ; but when this is not convenient, 
50 to 100 c.c. of milk may be drawn from each quarter 
directly into a sterile sample bottle, after discarding the 
first three expressions from each teat. In either case, the 
sample should be thoroughly mixed before the amount 
required for the test is drawn off. 

3. The volumeter, properly filled with water free 
from air bubbles, is closed at the top with a rubber stop- 
per and is then inserted into the perforated stopper of the 
bottle. The perforated stopper must be forced down 
sufficiently to close the small hole in the neck of the bot- 
tle. The fluids are mixed by gently whirling the bottle, 
care being taken not to wet the stopper. 

4. The apparatus is set aside at a temperature of 20 
to 25° C; in winter a water bath is necessary, but only 
the bottle should be placed in the water. The rubber 
stopper in the upper end of the volumeter should be re- 
moved in order to avoid any counter-pressure against 
the water being forced from the middle chamber of the 
volumeter to the outer by the pressure of the oxygen 
separated from the hydrogen peroxide in the bottle. The 
bottle is then permitted to stand for two hours, when the 
amount of oxygen is read off. 

5. The amount of oxygen separated is indicated by 
the extent to which the water in the inner tube of the 
volumeter has been forced downward. Before taking 
the reading as final, the bottle should be gently whirled 
until the volume of oxygen remains constant. Without 
such agitation, some of the gas may remain in the bottle, 
adherent to the fluid, and the reading will not give the 



METHODS OF EXAMINING MILK 291 

correct result. Increases of 0.3 to 1 c.c. have been ob- 
served after agitation. 

6. After the reading is taken, the volumeter is dis- 
connected from the bottle, the stopper inserted in the top, 
and the water forced from the outer to the middle tube 
by pressure on the stopper until the two columns of water 
are level with each other. The volumeter is then ready to 
be used again. The bottle is emptied and cleaned and 
sterilized for the next test. 

Milk from one or several cows in normal condition, 
tested within three hours after being drawn from the 
udder, will not show over 3 c.c. of oxygen at the end of 
the second hour. If the milk is not tested within three 
hours, the oxygen reading will be in excess of this figure, 
because the catalase in the milk at the time it was secreted 
will have been added to bj^ that produced by the bacteria 
in the milk. According to Faitelowitz and others, if 2 per 
cent, of chloroform is added to the milk the power or ac- 
tivity of the catalase existing at the time is not affected, 
while the secretion of catalase by bacteria is prevented. 

Certain physiological conditions cause an increase in 
the catalase. Colostrum, milk for 4 to 5 days up to 3 
weeks after calving, and milk from "strippers" yielding 
only a quart or less a day give a higher oxygen reading 
than is normal for milk at other stages of lactation. The 
oxygen reading is also increased after sudden or pro- 
nounced changes in feed, following incomplete milking 
and stasis of milk, and sometimes in oestrum when the 
cow is nervous and excitable. 

In disease of the udder, when individual milk is tested, 
the oxygen reading is above normal before any clinical 
symptoms are apparent and before there are any visible 
changes in the appearance of the milk. The reading 



292 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

continues high for a time after the chnical symptoms 
have disappeared. The increase of catalase in mastitis 
is not always due to the bacteria present. Koning has 
demonstrated that the streptococci of mastitis do not pro- 
duce catalase, but that the toxins they excrete irritate 
the gland tissue and cause an increased transudation of 
blood serum and emigration of leucocytes, thus increas- 
ing the catalase in the milk. The catalase may also be 
increased in purely traumatic or non-bacterial mastitis. 
When only one quarter of an udder is visibly diseased, 
the milk from the other quarters which are apparently 
healthy may show a high catalase reaction. The catalase 
test cannot be relied upon to discover mastitis when mixed 
milk is examined. Mixed milk containing 5 per cent, 
of milk from a diseased udder will show a high oxygen 
reading, but if the dilution is greater than this there will 
be nothing abnormal in the reaction (Gerber) . 

In general disease, and when disease is present in 
other organs than the udder, the oxygen reading of in- 
dividual milk is usually, but not always, high. In these 
conditions, according to Mogendorff, the catalase in the 
milk is increased when the udder assists in the elimina- 
tion of the products of disease, the toxins or other disease- 
products irritating the gland tissue and causing an un- 
usual amount of blood serum and leucocytes to pass over 
into the milk. The presence of pathological processes in 
the body is often indicated by an increase in the catalase 
in the milk before they are manifested by clinical symp- 
toms, while in diseases in which resolution is not complete 
the catalase may be increased in the milk after all clinical 
symptoms have disappeared. As a rule, there is an in- 
crease of catalase in the milk in all diseases accompanied 
by a high fever ; when non-encapsulated purulent areas 



METHODS OF EXAMINING MILK 293 

are present in the body, as in traumatic pericarditis, ab- 
scesses, f urunculosis, panaritium ; in diseases of the diges- 
tive apparatus such as gastro-intestinal catarrh, constipa- 
tion, tympanites, enteritis, etc. ; when the organs of elim- 
ination are affected, as in icterus, interference with the 
excretion of urine, constipation ; in acute and chronic in- 
flammation of the uterus ; in peritonitis, and in advanced 
tuberculosis, even when the udder is free from the disease. 
The catalase will also be increased in the milk of all cows 
reacting to tuberculin for several days after the injection. 

Whether a high catalase reaction is due to disease in 
the udder or to disease in another part of the body may 
be determined by centrifugalizing the milk and examin- 
ing the sediment. If the disease is in the udder, leuco- 
cytes will be present in excess of the usual number. 
Gratz and Naray observed that when the oxygen reading 
is high in the milk of cows which have recently "fresh- 
ened," the sediment, as obtained by the Trommsdorff 
method, may be low in volume but of a red color, the high 
catalase reaction being due to the presence of red blood 
cells. For a time following parturition, red blood cells 
may enter the milk by diapedesis or by rupture of blood 
vessels. They therefore regard it as necessary to examine 
the sediment before deciding as to the cause of a high 
catalase reaction. 

Fresh marJcet milk from cows in normal condition^ 
which has been properly cooled and cared for, should 
never show over 4 c.c. of oxygen at the end of the second 
hour (Gerber). IVhen market milk shows a higher 
oxygen reading, the indication is that the original bacter- 
ial contamination has been excessive, or that the milk is 
old, or that it may have pathological milk or colostrum 
mixed with it. A large amount of gas (CO2) will be 



294 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

separated if sodium bicarbonate has been used as a pre- 
servative. The catalase test is not as suitable for the ex- 
amination of market milk as some of the other methods, 
but it is one of the most delicate tests for detecting path- 
ological conditions when individual milk is examined. 
REDUCTASE TEST 

In this test, methylene blue solution and milk are 
mixed together and +he amount of reductase present, or 
the reduction power, is indicated by the length of time 
required for the blue color to disappear. Different prep- 
arations of methylene blue vary in composition and it is 
therefore recommended that Merck's B extra methylene 
blue be always used. The solution is prepared as fol- 
lows : methylene blue is added to absolute alcohol to sat- 
uration ; 5 c.c. of this saturated alcoholic solution is then 
added to 195 c.c. of sterile distilled water; this is the so- 
lution used in making the test. The saturated alcoholic 
solution is rather unstable, and Barthel and O. Jensen 
therefore recommend that the test solution be made with 
tablets of Merck's B extra methylene blue prepared by 
Blauenfeld and Tvede, of Copenhagen, Denmark. One 
tablet is dissolved in 200 c.c. of sterile distilled water. 
The solution will keep two weeks. When milk is tested 
with the tablet solution, the reduction time will be shorter 
than when it is tested with the solution made from the 
satui'ated alcoholic solution, because the tablet solution 
contains less methylene blue. 

Ordinary test tubes are used in making the test. 
These should be cleaned, plugged with cotton and steril- 
ized. The pipettes used in measuring the milk and the 
methlyene blue solution should also be cleaned and steril- 
ized. After each sample of milk is measured, the pipette 
used for this purpose should be rinsed with cold water 



METHODS OF EXAMINING MILK 295 

and sterilized by drawing boiling water into it several 
times. 

The test is made as follows : The milk to be tested is 
heatedtoatemperatm-eof 45to48' C. (113 to 118° F.) ; 
V2 c.e. of the methylene blue solution is placed in the 
test tube and 20 c.c. of the milk is added. The test tube is 
closed with the cotton plug, placed in a water bath or 
incubator at 38 to 39" C. (100.4 to 102° F.), and ob- 
served at frequent intervals to note the time of decolori- 
zation. If the methylene blue solution is placed in the 
tube first and the milk afterward, the two fluids will be 
thoroughly mixed and there will be no opportunity for 
a part of the methylene blue solution to be absorbed by 
the cotton plug. It is not necessarj^ to cover the mixture 
with a layer of paraffine oil, as was formerly recom- 
mended, because the difference in reduction time caused 
by the exclusion of oxygen is not sufficient to be taken 
into consideration in routine milk testing. 

Several investigators have compared the reduction 
time of market milk with the number of bacteria as de- 
termined by the plate method. O. Jensen, using a test 
solution prepared from a satm-ated alcoholic solution of 
methylene blue, found the relations to be as follows : 

1. Decolorization in 7 hours or over, 100,000 bacteria 
per c.c. 

2. Decolorization in from 2 to 7 hours, 100,000 to 
300,000 bacteria per c.c. 

3. Decolorization in from 14 to 2 hours, 800,000 to 
20,000,000 bacteria per c.c. 

4. Decolorization in less than i/4 hour, 49,000,000 to 
264,000,000 bacteria per c.c. 

In testing market milk with methylene blue solution 
prepared from tablets, O. Jensen and Barthel found the 



296 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

reduction time and the number of bacteria per c.c. to com- 
pare as follows : 

1. Decolor ization in 5% hours or over, less than 
500,000 bacteria per c.c. 

2. Decolorization in from 2 to 51/2 hours, 500,000 
to 4,000,000 bacteria per c.c. 

3. Decolorization in from 20 minutes to 2 hours, 
4,000,000 to 20,000,000 bacteria per c.c. 

4. Decolorization in 20 minutes or less, over 20,000,- 
000 bacteria per c.c. 

These figures do not apply to milk that has been 
heated. 

The reduction time of market milk agrees in a general 
way with the number of bacteria contained in the milk 
and is a very good index to the "keeping qualities" or 
stability of milk. The reductase test is not to be de- 
pended upon to detect pathological milk. While mastitis 
milk usually decolorizes in a shorter time than normal 
milk, this does not occur in all cases. 

O. Jensen has combined the reductase test with the 
fermentation test. 

FERMENTATION-REDUCTASE TEST 

This is a combination of the fermentation and re- 
ductase tests which was first proposed by O. Jensen. 
One-half c.c. of methylene blue solution is placed in a test 
tube with 20 c.c. of milk, the tube is placed in an incubator 
and kept under observation until decolorization occurs, 
as in the reductase test. In addition, the test tube is 
kept in the incubator until curdling occurs, and the type 
of curd is then noted. Methylene blue in large quantity 
inhibits the development of bacteria, especially the lactic 
acid bacteria, but in the quantity used in this test the 
effect is practically negligible. 



METHODS OF EXAMINING MILK 297 

A quickly reducing milk very frequently produces a 
good curd (jelly-like) because in milk rich in bacteria 
the lactic acid bacteria are often so numerous that they 
inhibit the growth of the other species. But a milk may 
reduce quickly and at the same time produce a bad curd 
(gaseous or peptonized) ; such milk is extremely objec- 
tionable. On the other hand, a slowly reducing milk may 
produce a peptonized curd. This is because milk pro- 
duced under cleanly conditions is exposed to a compara- 
tively slight bacterial contamination and the udder cocci 
consequently predominate. When such milk is kept at 
a low temperature the peptonizing bacteria (udder cocci) 
will develop more rapidly than the others and it will con- 
tain few lactic acid bacteria. For these reasons, it has 
been recommended by Barthel and O. Jensen that milk 
with a reduction time of 5y2 hours or over should not 
be condemned as bad on account of a peptonized curd. 

DIASTASE TEST 

Koning devised a method for the quantitative deter- 
mination of diastase. The reagents used are a solution of 
starch and a solution of iodine. The starch solution is 
prepared by adding 1 gramme of soluble starch to 100 c.c. 
of sterile distilled water, warming, and shaking the mix- 
ture to bring about solution. The iodine solution is pre- 
pared by dissolving 1 gramme of iodine and 2 grammes 
of potassium iodide in 300 c.c. of distilled water. The test 
is made as follows : 

Ten c.c. of milk is placed in each of five test tubes. 
0.05 c.c. of the starch solution is added to the first tube, 0.1 
c.c. to the second, 0.2 c.c. to the third, 0.25 c.c. to the 
fourth and 0.3 c.c. to the fifth. The tubes are placed in 
a water bath at 45° C. for 30 minutes, after which 1 c.c. 
of the iodine solution is added to each tube. If all of the 



298 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

starch has been digested the mixture in the tube assumes 
a citron-yellow color ; if any starch remains a blue color 
will appear. According to Koning, normal milk will 
digest the starch in the first two or the first three tubes ; 
a higher diastatic power indicates mastitis, while a lower 
indicates old milk. Others report that the diastatic power 
of milk from cows affected with mastitis is very variable 
and that the diastase test cannot therefore be depended 
upon to discover mastitis milk. The diastatic power is 
also increased in the colostral period and near the end of 
lactation. One observer affirms that the diastase in milk 
is decreased when the ration is rich in carbohydrates. 

TESTS FOR HEATED MILK 

Two tests are used to determine whether or not milk 
has been heated to 80° C. (176° F.) or above. They are 
as follows: 

StorcJis Test. — 5 c.c. of milk or cream is placed in a 
test tube, 1 drop of 0.2 per cent, solution of hydrogen 
peroxide containing 0.1 per cent, of sulphuric acid, and 
2 drops of a 2 per cent, solution of paraphenyldiamin are 
added, and the mixture is shaken. If the mixture as- 
sumes an indigo blue or violet color immediately, it has 
not been heated at all or not higher than 78° C. (172.5° 
F. ) ; if it becomes a light bluish-gray within a half min- 
ute, it has been heated to between 79 and 80° C. (174.2° 
to 176° F.) ; if it remains white, it has been heated to at 
least 80° C. (176° F.) . Raw whey gives a violet or red- 
dish-brown color. 

Arnold's Guaiac Test. — "A. small quantity of milk is 
placed in a test tube and a little tincture of guaiac is run 
down the side of the tube drop by drop so that it will 
not mix with the milk but form a layer on top of the milk. 
If the milk is raw or has not been heated to 80° C. 



METHODS OF EXAMINING MILK 299 

(176° F.), a blue ring is formed at the point of contact 
of the two fluids. If the milk has been heated to 80° C. 
( 176° F. ) or above, no color change occurs. The guaiac- 
wood tincture is more reliable than the guaiac-resin tinc- 
ture of the U. S. Pharmacopoeia. The addition of a few 
drops of a weak aqueous solution of hydrogen peroxide 
after the tincture of guaiac has been run into the test 
tube increases the reliability and sharpness of the test 
(Zinc), although if the guaiac tincture is "ripe," a 
change which takes place with age, the hydrogen peroxide 
is not necessary. When the test is made with the tinc- 
ture alone, the activity of the latter should be tested 
against known raw milk. If the hydrogen peroxide is 
added to the milk before the guaiac tincture, or if too 
much is added, the reaction will be retarded or suppressed. 
When milk is strongly acid it will not give the color 
reaction at all, or the reaction will be faint or delayed. 
Lime water should be added to such milk and to butter- 
milk before testing. Cold milk may not react at all 
or very slowly. An excess of hydrogen peroxide will pre- 
vent the reaction. Heated milk to which formalin has 
been added will give a color reaction to the Storch test 
like raw milk, but formalin has no influence on the guaiac 
test when it is present in the quantity used to preserve 
milk. The guaiac test is also not affected by sodium 
bicarbonate, borax, boric acid, and salicylic acid, but the 
presence of potassium bichromate causes heated milk to 
react like raw milk and intensifies the color reaction of 
raw milk. 

EXAMINATION FOR DIRT 
The milk is filtered through small cotton discs and 
the larger particles of dirt present are collected on the 
surface of the disc. There are several different forms of 



300 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

apparatus for making this test. In some the milk is 
permitted to flow through the filter by gravity, while in 
the others it is forced through by air pressure from a 
rubber bulb. According to the quantity of dirt collected 
on the cotton disc the milk is classed as good, medium, 
fair, and bad. The discs are sometimes dried and mailed 
to the producer for his examination. There is no direct 
relation between the quantity of dirt collected on the cot- 
ton disc and the bacterial content. Milk which would be 
classed as good according to this test may have a high 
bacterial content and vice versa. Furthermore, milk pro- 
duced under unclean conditions will test "good " by this 
test if it is well strained beforehand. 

Another method of testing for dirt is to place the 
milk in a conical glass, or in a vessel with a narrow tube 
at the bottom, and measure the volume of sediment which 
settles to the bottom after a certain period ; or the milk 
may be centrifugalized and the sediment measured. 

The visible dirt in milk consists principally of par- 
ticles of feed and litter, manure, hairs, dandruff and dust. 

TEST FOR LACTOSE 

Glage has devised a simple test for lactose which may 
be applied to samples of individual cow's milk or to 
samples of milk from the different quarters of the udder. 
It is made as follows : Place 3 c.c. of milk and 3 c.c. of 
a 15 per cent, solution of potassium hydroxide in a test 
tube, boil thoroughly and let stand for 10 minutes. When 
the milk contains the normal amount of lactose the mix- 
ture at first becomes pale yellow during the boiling, 
changing quickly to dark yellow, to orange, and then 
to brown ; after standing the color of the mixture becomes 
coffee-brown or red-brown. If the quantity of lactose is 




oeRBER'S 


IMPROVED TESTER 


TESTER. WITH 


TESTEfL. 


EOIMENT 


WITH 


COVER, AND 


WITH 


TESTER. 


STEAM JACKET 


RUBBER. aULB 


PUJN6EP.. 






Fig. 41. — Various types of dirt testers (Wisconsin Exp. Station Cir. No. 41). 



METHODS OF EXAMINING MILK 301 

below normal the color remains yellow or orange. When 
the color becomes yellowish-brown the condition of the 
milk must be regarded as doubtful. The presence of a 
large amount of fat is likely to interfere with the reaction 
and it is therefore best to remove the fat from the milk 
before applying the test. Milk sugar^ is decreased in 
quantity and is sometimes entirely absent in inflamma- 
tion of the udder. It is also reduced in quantity during 
the colostral period and toward the end of lactation; 
exercise sometimes decreases it. It is present in greatest 
amount in the middle of a milking and lowest at the 
beginning and end. Fresh market milk will always give 
a normal reaction to this test. 

EXAMINATION FOR COLORING MATTERS 

When the yellow color of milk is natural it is largely 
confined to the cream, and if opportunity is given for 
the cream to rise the milk beneath it has a bluish tinge. 
But when the yellow color is artificial not only the cream 
but the milk beneath it is of the same color. Artificial 
coloring matters are sometimes added to milk to give it 
a rich color when it has been adulterated with water. 
Annatto, also called arnatto and annotto ; analin orange, 
an azo-dye, and caramel are the substances most fre- 
quently used. Leach recommends the following pro- 
cedure for the detection of artificial coloring: 

Place 150 c.c. of milk in a casserole, add a little acetic 
acid and heat until curdling occurs. Gather the curd 
together with a glass rod and pour off the whey, or sepa- 
rate by filtration. Macerate the curd with ether in a 
stoppered bottle for several hours. Evaporate the ether 
extract on a water bath, add sufficient sodimn hydroxide 
to the residue to make it alkaline and pour the mixture 



302 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

upon a small wet filter, wash the fat off the surface with 
tap water and dry the filter. If the filter paper is colored 
orange the presence of annatto is indicated. The appli- 
cation of stannous chloride will change the color to a 
characteristic pink if annatto is present. 

If the curd is colorless after it has been extracted 
with ether no other coloring matter is present. If it 
is orange or brownish the presence of analin orange or 
caramel is indicated. The curd is then shaken in a test 
tube with concentrated hydrochloric acid. If the solu- 
tion immediately turns pink the presence of analin orange 
is indicated. If it slowly turns blue, this points to the 
presence of caramel and the following test should be 
applied: About 120 c.c. of the milk and an equal quan- 
tity of alcohol are mixed together and filtered. A small 
quantity of subacetate of lead is added to the filtrate and 
the precipitate produced is collected on a small paper 
filter which is dried in an atmosphere free from hydrogen 
sulphide. If caramel is present the precipitate is of a 
dark brown color. If no caramel is present the pre- 
cipitate will be white or straw color. 



APPENDIX 

METHODS AND STANDARDS FOR THE PRODUC- 
TION AND DISTRIBUTION OF 
" CERTIFIED MILK " i 

Adopted by the American Association of Medical Milk Commissions, 

May 1, 1912. 

Certified milk is the product of dairies operated in accord- 
ance with accepted rules and regulations formulated by author- 
ized medical milk commissions to insure its purity and adapta- 
bility for infants and invalids. 

The need for such a milk was experienced primarily by those 
engaged in the conservation of the life and health of infants. As 
a result there was formulated in 1892 a plan whereby certified 
milk would be produced by a dairyman under the control of a 
medical milk commission designated by a representative medical 
society. 

^ At the fifth annual meeting of the American Association 
of Medical Milk Commissions, held in Philadelphia, May 25, 
1911, a committee was appointed to revise the manual of work- 
ing methods and standards for the guidance of medical milk 
commissions in the supervision of the production and distribution 
of certified milk. The committee consisted of Dr. J. W. Kerr 
(chairman), Dr. S. McC. Hamill, and Dr. Henry L. Coit. 
This, their report, was adopted at the sixth annual meeting, 
held at Louisville, Kentucky, May 1, 1912, as the working 
methods and standards of the association. The association 
recommends them to component commissions as ideal and to be 
as closely approximated as possible. The report includes a 
statement concerning the certified milk movement, as well as 
the revised methods and standards, and is published for the 
information of those Interested In the improvement of public 
milk supplies. 

Reprint from the Public Health Reports, vol. xxvii. No. 24, 
June 14, 1912. 

303 



304 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

The first rules designed for this purpose were those contained 
in an agreement entered into by a medical milk commission and 
the dairyman concerned.^ 

The rules contained in the original agreement mentioned rep- 
resented the essential requirements for the production of certified 
milk. Following this precedent, other commissions were organ- 
ized, which, in 1906, became federated into a national associa- 
tion known as the American Association of Medical Milk Com- 
missions. 

A fundamental object of this Association was to bring about 
the uniformity of standards and their perfection. This result 
has been reached by the adoption from time to time of definite 
standards relating to the veterinary inspection of herds and 
farms, the medical inspection of employees handling the milk, 
and the bacteriological and chemical examinations as to quality 
and purity. The requirements with respect to these four topics 
have been previously reported upon by committees and adopted 
by the Association, and at its last annual meeting provision 
was made for their further revision and amplification. 

ORGANIZATION OF MEDICAL MILK COMMISSIONS 
The Medical Milk Commission is appointed by a representa- 
tive medical society, and acts under its auspices and for it, to 
encourage the production of milk of the highest possible stand- 
ards of purity. No commission should be considered as certi- 
fying milk that does not conform to the standards adopted from 
time to time by the Association of Medical Milk Commissions. 
The commission should include at least five members or a num- 
ber sufficient to become responsible for and to carry on the follow- 
ing divisions of work ; (a) The hygiene of the dairy, as it relates 
to the production and distribution of the milk; (b) the veteri- 
nary supervision of the herd; (c) the medical supervision of the 
employees; (d) the chemical and bacteriological examinations 
of the milk. 

^ Bui. 56, Hygienic Laboratory, Public Health and Marine 
Hospital Service, p. 615. 



APPENDIX 305 

DUTIES OF THE COMMISSION 

After its organization the commission should designate a 
veterinarian, a physician, a chemist, and a bacteriologist to en- 
force its methods and standards, which shall be the prevailing 
methods and standards of the American Association of Medical 
Milk Commissions, and these officers should be required to render 
regular reports of their inspections and examinations. A uni- 
form written agreement should then be entered into with any 
dairyman who is desirous of undertaking the production of 
certified milk and the investigation of whose plant shows it to 
be properly equipped for such purpose. Such agreement shall 
require the observance of the methods and standards hereinafter 
mentioned. 

Upon receipt of favorable reports from the several experts 
and committees which have made the investigations, the dairy- 
man should be authorized, in accordance with the terms of the 
agi'eement, to employ the term " Certified Milk," and he shall be 
required to attach to all containers of any character used in dis- 
tributing the milk produced under the agreement a certificate or 
seal bearing the term " Certified Milk," the name of the medical 
milk commission certifying it, and the day or date of production 
of the milk contained therein. 

HYGIENE OF THE DAIRY 
Under the Supervision and Control of the Veterinarian 

1. Pastures or Paddocks. — Pastures or paddocks to which 
the cows have access shall be free from marshes or stagnant pools, 
crossed by no stream which might become dangerously con- 
taminated, at sufficient distances from offensive conditions to 
suffer no bad effects from them, and shall be free from plants 
which affect the milk deleteriously. 

2. Surroundings of Buildings. — The surroundings of all 
buildings shall be kept clean and free from accumulations of 
dirt, rubbish, decayed vegetable or animal matter or animal 
waste, and the stable yard shall be well drained. 

3. Location of Buildings. — Buildings in which certified milk 
is produced and handled shall be so located as to insure proper 

20 



306 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

shelter and good drainage, and at sufficient distance from other 
buildings, dusty roads, cultivated and dusty fields, and all other 
possible sources of contamination; provided, in the case of un- 
avoidable proximity to dusty roads or fields, the exposed side 
shall be screened with cheese cloth. 

4. Construction of Stables. — The stables shall be con- 
structed so as to facilitate the prompt and easy removal of waste 
products. The floors and platforms shall be made of cement or 
other non-absorbent material, and the gutters of cement only. 
The floors shall be properly graded and drained, and the manure 
gutters shall be from six to eight inches deep and so placed in 
relation to the platform that all manure will drop into them. 

5. The inside surface of the walls and all interior construc- 
tion shall be smooth, with tight joints, and shall be capable of 
shedding water. The ceiling shall be of smooth material and 
dust-tight. All horizontal and slanting surfaces which might 
harbor dust shall be avoided. 

6. Drinhing and Feed Troughs. — Drinking troughs or 
basins shall be drained and cleaned each day, and feed troughs 
and mixing floors shall be kept in a clean and sanitary condition. 

7. Stanchions. — Stanchions when used shall be constructed 
of iron pipes or hardwood, and throat latches shall be provided 
to prevent the cows from lying down between the time of cleaning 
and the time of milking. 

8. Ventilation. — The cow stables shall be provided with ade- 
quate ventilation either by means of some approved artificial 
device, or by the substitution of cheesecloth for glass in the 
windows, each cow to be provided with a minimum of 600 cubic 
feet of air space. 

9. Windows. — A sufficient number of windows shall be in- 
stalled and so distributed as to provide satisfactory light and a 
maximum of sunshine; two feet square of window area to each 
600 cubic feet of air space to represent the minimum. The cover- 
ings of such windows shall be kept free from dust and dirt. 

10. Exclusion of Flies, etc. — All necessary measures should 
be taken to prevent the entrance of flies and other insects, and 
rats and other vermin into all the buildings. 

11. Exclusion of Animals from the Herd. — No horses, hogs, 



APPENDIX 307 

dogs, or other animals or fowls shall be allowed to come in con- 
tact with the certified herd, either in the stables or elsewhere. 

12. Bedding. — No dusty or mouldy hay or straw, bedding 
from horse stalls, or other unclean materials shall be used for 
bedding the cows. Only bedding which is clean, dry, and 
absorbent may be used, preferably shavings or straw. 

13. Cleaning Stable and Disposal of Manure. — Soiled bed- 
ding and manure shall be removed at least twice daily, and the 
floors shall be swept and kept free from refuse. Such cleaning 
shall be done at least one hour before the milking time. Manure, 
when removed, shall be drawn to the field or temporarily stored 
in containers so screened as to exclude flies. Manure shall not 
be even temporarily stored within 300 feet of the barn or 
dairy building. 

14. Cleaning of Cows. — Each cow in the herd shall be 
groomed daily, and no manure, mud, or filth shall be allowed to 
remain upon her during milking ; for cleaning, a vacuum appa- 
ratus is recommended. 

15. Clipping. — Long hairs shall be clipped from the udder 
and flanks of the cow, and from the tail above the brush. The 
hair on the tail shall be cut so that the brush may be well above 
the ground. 

16. Cleaning of Udders. — The udders and teats of the cow 
shall be cleaned before milking ; they shall be washed with a cloth 
and water, and wiped dry with another clean sterilized cloth — 
a separate cloth for drying each cow. 

17. Feeding. — All foodstuffs shall be kept in an apartment 
separate from and not directly communicating with the cow 
barn. They shall be brought into the barn only immediately 
before the feeding hour, which shall follow the milking. 

18. Only those foods shall be used which consist of fresh, 
palatable, or nutritious materials, such as will not injure the 
health of the cows or unfavorably affect the taste or character 
of the milk. Any dirty or mouldy food or food in a state of 
decomposition or putrefaction shall not be given. 

19. A well-balanced ration shall be used, and all changes of 
food shall be made slowly. The first few feedings of grass, 



308 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

alfalfa, ensilage, green corn, or other green feeds shall be given 
in small rations and increased gradually to full ration. 

20. Exercise. — All dairy cows shall be turned out for exer- 
cise at least two hours in each twenty-four in suitable weather. 
Exercise yards shall be kept free from manure and other filth. 

21. Washing of Hands. — Conveniently located facilities 
shall be provided for the milkers to wash in before and during 
milking. 

22. The hands of the milkers shall be thoroughly washed 
with soap, water, and bru^-h, and carefully dried on a clean towel 
immediately before milking. The hands of the milkers shall be 
rinsed with clean water and carefully dried before milking each 
cow. The practice of moistening the hands with milk is for- 
bidden. 

23. Milking Clothes. — Clean overalls, jumper, and cap shall 
be worn during milking. They shall be washed or sterilized each 
day and used for no other purpose, and when not in use they 
shall be kept in a clean place, protected from dust and dirt. 

24). Things to be Avoided hy Milkers. — ^While engaged about 
the dairy or in handling the milk, employees shall not use 
tobacco nor intoxicating liquors. They shall keep their fingers 
away from their nose and mouth, and no milker shall permit his 
hands, fingers, lips, or tongue to come in contact with milk 
intended for sale. 

25. During milking the milkers shall be careful not to 
touch anything but the clean top of the milking stool, the milk 
pail and the cow's teats. 

26. Milkers are forbidden to spit upon the walls or floors 
of stables, or upon the walls or floors of milk houses, or into the 
water used for cooling the milk or washing the utensils. 

27. Fore-Milk. — The first streams from each teat shall be 
rejected, as this fore-milk contains large numbers of bacteria. 
Such milk shall be collected into a separate vessel and not milked 
onto the floor or into the gutters. The milking shall be done 
rapidly and quietly, and the cows shall be treated kindly, 

28. Milk and Calving Period. — Milk from all cows shall be 
excluded for a period of forty-five days before and seven days 
after parturition. 



APPENDIX 309 

29. Bloody and Stringy Milh. — If milk from any cow is 
bloody and stringy, or of unnatural appearance, the milk from 
that cow shall be rejected and the cow isolated from the herd 
until the cause of such abnormal appearance has been determined 
and removed, especial attention being given in the meantime to 
the feeding or to possible injuries. If dirt gets into the pail, the 
milk shall be discarded and the pail washed before it is used. 

30. Make-up of Herd. — No cows except those receiving the 
same supervision and care as the certified herd shall be kept in 
the same barn or brought in contact with them. 

31. Employees Other Than Milkers. — The requirements for 
milkers, relative to garments and cleaning of hands, shall apply 
to all other persons handling the milk, and children unattended 
by adults shall not be allowed in the dairy nor in the stable 
during milking. 

32. Straining and Strainers. — Promptly after the milk is 
drawn it shall be removed from the stable to a clean room and 
then emptied from the milk pail to the can, being strained 
through strainers made of a double layer of finely meshed 
cheesecloth or absorbent cotton thoroughly sterilized. Several 
strainers shall be provided for each milking in order that they 
may be frequently changed. 

33. Dairy Building. — A dairy building shall be provided 
which shall be located at a distance from the stable and dwelling 
prescribed by the local commission, and there shall be no 
hog-pen, privy, or manure pile at a higher level or within 300 
feet of it. 

34. The dairy building shall be kept clean and shall not be 
used for purposes other than the handling and storing of milk 
and milk utensils. It shall be provided with light and ventila- 
tion, and the floors shall be graded and water-tight. 

35. The dairy building shall be well lighted and screened, 
and drained through well-trapped pipes. No animals shall be 
allowed therein. No part of the dairy building shall be used 
for dwelling or lodging purposes, and the bottling room shall be 
used for no other purpose than to provide a place for clean 
milk utensils and for handling the milk. During bottling this 
room shall be entered only by persons employed therein. The 



310 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

bottling room shall be kept scrupulously clean and free from 
odors. 

36. Temperature of Milk. — Proper cooling to reduce the 
temperature to 45° F. shall be used, and aerators shall be so 
situated that they can be protected from flies, dust, and odors. 
The milk shall be cooled immediately after being milked, and 
maintained at a temperature between 35° and 45° F. until 
delivered to the consumer. 

37. Sealing of Bottles. — Milk, after being cooled and bot- 
tled, shall be immediately sealed in a manner satisfactory to 
the commission, but such seal shall include a sterile hood 
which completely covers the lip of the bottle. 

38. Cleaning and Sterilizing of Bottles. — The dairy building 
shall be provided with approved apparatus for the cleansing and 
sterilizing of all bottles and utensils used in milk production. 
All bottles and utensils shall be thoroughly cleaned by hot 
water and sal soda, or equally pure agent, rinsed until the 
cleaning water is thoroughly removed, then exposed to live 
steam or boiling water at least twenty minutes, and then kept 
inverted until used, in a place free from dust and other con- 
taminating materials. 

39. Utensils. — All utensils shall be so constructed as to be 
easily cleaned. The milk pail should preferably have an ellip- 
tical opening five by seven inches in diameter. The cover of 
this pail should be so convex as to make the entire interior of the 
pail visible and accessible for cleaning. The pail shall be made 
of heavy seamless tin, and with seams which are flushed and 
made smooth by solder. Wooden pails, galvanized-iron pails, 
or pails made of rough, porous materials, are forbidden. All 
utensils used in milking shall be kept in good repair. 

40. Water Supply. — The entire water supply shall be abso- 
lutely free from contamination, and shall be sufficient for all 
dairy purposes. It shall be protected against flood or surface 
drainage, and shall be conveniently situated in relation to the 
milk house. 

41. Privies, etc., in Relation to Water Supply. — Privies, 
pig-pens, manure piles, and all other possible sources of con- 
tamination shall be so situated on the farm as to render im- 



APPENDIX 311 

possible the contamination of the water supply, and shall be so 
protected by use of screens and other measures as to prevent 
their becoming breeding grounds for flies. 

42. Toilet Rooms. — Toilet facihties for the milkers shall be 
provided and located outside of the stable or milk house. These 
toilets shall be properly screened, shall be kept clean, and shall 
be accessible to wash basins, water, nail brush, soap, and towels, 
and the milkers shall be required to wash and dry their hands 
immediately after leaving the toilet room. 

TRANSPORTATION 
4fS. In transit, the milk packages shall be kept free from dust 
and dirt. The wagon, trays, and crates shall be kept scrupulously 
clean. No bottles shall be collected from houses in which com- 
municable diseases prevail, unless a separate wagon is used and 
under conditions prescribed by the department of health and the 
medical milk commission. 

44. All certified milk shall reach the consumer within thirty 
hours after milking. 

VETERINARY SUPERVISION OF THE HERD 

45. Tuberculin Test. — The herd shall be free from tubercu- 
losis, as shown by the proper application of the tuberculin test. 
The test shall be applied in accordance with the rules and regu- 
lations of the United States Government, and all reactors shall 
be removed immediately from the farm.^ 

46. No new animals shall be admitted to the herd without 
first having passed a satisfactory tuberculin test, made in 
accordance with the rules and regulations mentioned ; the tuber- 
culin to be obtained and applied only by the official veterinarian 
of the commission. 

47. Immediately following the application of the tuberculin 
test to a herd for the purpose of eliminating tuberculous cattle, 
the cow stable and exercising yards shall be disinfected by the 
veterinary inspector in accordance with the rules and regula- 
tions of the United States Government.^ 

^ See circular of Instructions issued by the Bureau of Animal 
Industry for making tuberculin tests and for disinfection of 
premises. 



312 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

48. A second tuberculin test shall follow each primary test 
after an interval of six months, and shall be applied in accord- 
ance with the rules and regulations mentioned. Thereafter, 
tuberculin tests shall be reapplied annually, but it is recom- 
mended that the retests be applied semi-annually. 

49. Identification of Cows. — Each dairy cow in each of the 
certified herds shall be labeled or tagged with a number or mark 
which will permanently identify her. 

50. Herd-hook Record. — Each cow in the herd shall be 
registered in a herd booK, which register shall be accurately 
kept so that her entrance and departure from the herd and her 
tuberculin testing can be identified. 

51. A copy of this herd-book record shall be kept in the 
hands of the veterinarian of the medical milk commission under 
which the dairy farm is operating, and the veterinarian shall 
be made responsible for the accuracy of this record. 

52. Dates of Tuberculin Tests. — The dates of the annual 
tuberculin tests shall be definitely arranged by the medical milk 
commission, and all of the results of such tests shall be recorded 
by the veterinarian and regularly reported to the secretary of 
the medical milk commission issuing the certificate. 

53. The results of all tuberculin tests shall be kept on file by 
each medical milk commission, and a copy of all such tests shall 
be made available to the American Association of Medical Milk 
Commissions for statistical purposes. 

54. The proper designated officers of the American Associa- 
tion of Medical Milk Commissions should receive copies of 
reports of all of the annual, semiannual, and other official tuber- 
culin tests which are made, and keep copies of the same on file 
and compile them annually for the use of the association. 

55. Disposition of Cows Sick with Diseases Other Than 
Tuberculosis. — Cows having rheumatism, leucorrhoea, inflamma- 
tion of the uterus, severe diarrhoea, or disease of the udder, or 
cows that from any other cause may be a menace to the herd, 
shall be removed from the herd, placed in a building separate 
from that which may be used for the isolation of cows with 
tuberculosis, unless such building has been properly disinfected 
since it was last used for this purpose. The milk from such cows 



APPENDIX 313 

shall not be used, nor shall the cows be restored to the herd until 
permission has been given by the veterinary inspector after a 
careful physical examination. 

56. Notification of Veterinary Inspector. — In the event of 
the occurrence of any of the diseases just described between the 
visits of the veterinary inspector, or if at any time a number of 
cows become sick at one time in such a way as to suggest the 
outbreak of a contagious disease or poisoning, it shall be the 
duty of the dairyman to withdraw such sickened cattle from the 
herd, to destroy their milk, and to notify the veterinary inspector 
by telegraph or telephone immediately. 

57. Emaciated Cows. — Cows that are emaciated from 
chronic diseases or from any cause that in the opinion of the 
veterinary inspector may endanger the quality of the milk, shall 
be removed from the herd. 

BACTERIOLOGICAL STANDARDS 

58. Bacterial Counts. — Certified milk shall contain less than 
10,000 bacteria per cubic centimetre when delivered. In case a 
count exceeding 10,000 bacteria per cubic centimetre is found, 
daily counts shall be made, and if normal counts are not 
restored within ten days the certificate shall be suspended. 

59. Bacterial counts shall be made at least once a week. 

60. Collection of Samples. — The samples to be examined 
shall be obtained from milk as offered for sale, and shall be 
taken by a representative of the milk commission. The samples 
shall be received in the original packages, in properly iced 
containers, and they shall be so kept until examined, so as to 
limit as far as possible changes in their bacterial content. 

61. For the purpose of ascertaining the temperature, a sep- 
arate original package shall be used, and the temperature 
taken at the time of collecting the sample, using for the purpose 
a standardized thermometer graduated in the centigrade scale. 

62. Interval Between Milking and Plating. — The examina- 
tions shall be made as soon after collection of the samples as 
possible, and in no case shall the interval between milking and 
plating the samples be longer than forty hours. 

63. Plating. — The packages shall be opened with aseptic 



314 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

precautions after the milk has been thoroughly mixed by vigor- 
ously reversing and shaking the container twenty-five times. 

64. Two plates at least shall be made for each sample of 
milk, and there shall also be made a control of each lot of 
medium and apparatus used at each testing. The plates shall 
be grown at 37° C. for forty-eight hours. 

65. In making the plates there shall be used agaragar media 
containing 1.5 per cent, agar and giving a reaction of 1.0 to 
phenolphthalein. 

[The method recommended by a committee of the American 
Public Health Association for the making of the medium is to 
be followed (see page 262), modified, however, as to the agar 
content and reaction to conform to the requirements specified 
in section 65.1 

66. Samples of milk for plating shall be diluted in the pro- 
portion of 1 part of milk to 99 parts of sterile water; shake 
25 times and plate 1 c.c. of the solution. 

[The recommendations of the committee of the American 
Public Health Association in regard to plating are to be fol- 
lowed (see page 265). 1 

67. Determination of Taste and Odor of Milk.— After the 
plates have been prepared and placed in the incubator, the 
taste and odor of the milk shall be determined after warming 
the milk to 100° F.^ 

68. Counts. — The total number of colonies on each plate 
should be counted, and the results expressed; in multiples of the 
dilution factor. Colonies too small to be seen with the naked 
eye or with slight magnification shall not be considered in the 
count. 

69. Records of Bacteriologic Tests. — The results of all bac- 
terial tests shall be kept on file by the secretary of each commis- 
sion, copies of which should be made available annually for the 
use of the American Association of Medical Milk Commissions. 

* Should it be deemed desirable and necessary to conduct 
tests for sediment, the presence of special bacteria, or the num- 
ber of leucocytes, the methods adopted by the committee of the 
American Public Health Association should be followed. 



APPENDIX 315 

CHEMICAL STANDARDS AND METHODS 
The methods that must be followed in carrying out the chem- 
ical investigations essential to the protection of certified milk 
are so complicated that in order to keep the fees of the chemist 
at a reasonable figure there must be eliminated from the exam- 
ination those procedures which, whilst they might be helpful and 
interesting, are in no sense necessary. 

For this reason the determination of the water, the total 
solids, and the milk sugar is not required as a part of the routine 
examination. 

70. The chemical analyses shall be made by a competent 
chemist designated by the medical milk commission. 

71. Method of Ohtavning Samples. — The samples to be ex- 
amined by the chemist shall have been examined previously by 
the bacteriologist designated by the medical milk commission 
as to temperature, odor, taste, and bacterial content. 

72. Fat Standards. — The fat standard for certified milk 
shall be 4 per cent., with a permissible range of variation of 
from 3.5 to 4.5 per cent. 

73. The fat standard for certified cream shall be not less 
than 18 per cent. 

74. If it is desired to sell higher fat-percentage milks or 
creams as certified milks or creams, the range of variation for 
such milks shall be 0.5 per cent, on either side of the advertised 
percentage and the range of variations for such creams shall be 
2 per cent, on either side of the advertised percentage. 

75. The fat content of certified milks and creams shall be 
determined at least once each month. 

76. The methods recommended for this purpose are the 
Babcock (a), the LefFmann-Beam (5), and the Gerber (c). 
(See pages 233 to 239.) 

77. Before condemning samples of milk which have fallen 
outside the limits allowed, the chemist shall have determined, by 
control ether extractions, that his apparatus and his technic 
are reliable. 

78. Protein Standard. — The protein standard for certified 
milk shall be 3.50 per cent., with a permissible range of varia- 
tion of from 3 to 4 per cent. 



316 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

79. The protein standard for certified cream shall corre- 
spond to the protein standard for certified milk. 

80. The protein content shall be determined only when any 
special consideration seems to the medical milk commission to 
make it desirable. 

81. It shall be determined by the Kjeldahl method, using 
the Gunning or some other reliable modification, and employing 
the factor 6.25 in reckoning the protein from the nitrogen. 

Kjeldahl Method. — Five cubic centimetres are measured 
carefully into a flat-bottoxn 800 c.c. Jena flask, 20 c.c. of concen- 
trated sulphuric acid (C. P.; sp. gr., 1.84) are added, and 0.7 
gramme of mercuric oxide (or its equivalent in metallic mer- 
cury) ; the mixture is then heated over direct flame until it is 
straw-colored or perfectly white; a few crystals of potassium 
permianganate are now added till the color of the liquid remains 
green. All the nitrogen in the milk has then been converted 
into the form of ammonium sulphate. After cooling, 200 c.c. 
of ammonia-free distilled water are added, 20 c.c. of a solution of 
potassium sulphide (containing 40 grammes sulphide per litre), 
and a fraction of a gramme of powdered zinc. A quantity of 
semi-normal HCl solution more than sufficient to neutralize the 
ammonia obtained in the oxidation of the milk is now carefully 
measured out from a delicate burette (divided into 1/20 c.c.) 
into an Erlenmeyer flask and the flask connected with a distil- 
lation apparatus. At the other end the Jena flask containing 
the watery solution of the ammonium sulphate is connected, 
after adding 50 c.c. of a concentrated soda solution (1 pound 
'*pure potash" dissolved in 500 c.c. of distilled water and allowed 
to settle) ; the contents of the Jena flask are now heated to 
boiling, and the distillation is continued for 40 minutes to an 
hour, until all ammonia has been distilled over. 

The excess of acid in the Erlenmeyer receiving flask is then 
accurately titrated back by means of a tenth-normal standard 
ammonia solution, using a cochineal solution as an indicator. 
From the amount of acid used the per cent, of nitrogen is ob- 
tained; and from it the per cent, of casein and albumen in the 
milk by multiplying by 6.25. The amount of nitrogen contained 
in the chemicals used is determined by blank experiments and 



APPENDIX 317 

deducted from the nitrogen obtained as described. (Farrington 
and Woll, Testing Milk and Its Products, p. 221.) 

82. Coloring Matter and Preservatives. — All certified milks 
and creams shall be free from adulteration, and coloring matter 
and preservatives shall not be added thereto. 

83. Tests for the detection of added coloring matter shall be 
applied whenever the color of the milk or cream is such as to 
arouse suspicion. 

Test for Coloring Matter. — The presence of foreign color- 
ing matter in milk is easily shown by shaking 10 c.c. of the milk 
with an equal quantity of ether ; on standing, a clear ether solu- 
tion will rise to the surface ; if artificial coloring matter has been 
added to the milk, the solution will be yellow colored, the inten- 
sity of the color indicating the quantity added; natural fresh 
milk will give a colorless ether solution. (Testing Milk and Its 
Products, Farrington and Woll, p. 244.) 

84. Tests for the detection of formaldehyde, borax, and 
boracic acid shall be applied at least once each month. Occa- 
sionally application of tests for the detection of salicylic acid, 
benzoic acid, and the benzoates are also recommended. (See 
pages 257 to 260.) 

85. Detection of Heated Milk. — Certified milk or cream 
shall not be subjected to heat unless specially directed by the 
commission to meet emergencies. 

86. Tests to determine whether such milks and creams have 
been subjected to heat shall be applied at least once each month. 
(See page 298.) 

87. Specific Gravity. — The specific gravity of certified milk 
shall range from 1.029 to 1.034. 

88. The specific gravity shall be determined at least each 
month. (See page 228.) 

METHODS AND REGULATIONS FOR THE MEDICAL EXAMINA- 
TION OF EMPLOYEES, THEIR HEALTH AND 
PERSONAL HYGIENE 

89. A medical officer known as the attending dairy physi- 
cian shall be elected by the commission, who should reside near 
the dairy producing certified milk. He shall be a physician 
in good standing and authorized by law to practice medicine; 



318 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

he shall be responsible to the commission and subject to its direc- 
tion. In case more than one dairy is under the control of the 
commission and they are in different localities, a separate 
physician should be designated for employment for the super- 
vision of each dairy. 

90. Before any person shall come on the premises to live 
and remain as an employee, such person, before being engaged 
in milking or the handling of milk, shall be subjected to a com- 
plete physical examination by the attending physician. No per- 
son shall be employed who has not been vaccinated recently or 
who upon examination is found to have a sore throat, or to 
be suffering from any form of tuberculosis, venereal disease, 
conjunctivitis, diarrhoea, dysentery, or who has recently 
had typhoid fever or is proved to be a typhoid carrier, or who 
has any inflammatory disease of the respiratory tract, or any 
suppurative process or infectious skin eruption, or any disease 
of an infectious or contagious nature, or who has recently been 
associated with children sick with contagious disease. 

91. In addition to ordinary habits of personal cleanliness, all 
milkers shall have well-trimmed hair, wear close-fitting caps, and 
have clean-shaven faces. 

92. When the milkers live upon the premises their dormi- 
tories shall be constructed and operated according to plans 
approved by the commission. A separate bed shall be provided 
for each milker, and each bed shall be kept supplied with clean 
bedclothes. Proper bathing facilities shall be provided for all 
employees on the dairy premises, preferably a shower bath, 
and frequent bathing shall be enjoined. 

93. In case the employees live on the dairy premises, a 
suitable building shall be provided to be used for the isolation 
and quarantine of persons under suspicion of having a con- 
tagious disease. 

The following plan of construction is recommended: 

The quarantine building and hospital should be one story 

high and contain at least two rooms, each with a capacity 

of about 6000 cubic feet and containing not more than three 

beds each, the rooms to be separated by a closed partition. The 



APPENDIX 319 

doors opening into the rooms should be on opposite sides of 
the building, and provided with locks. The windows should be 
barred and the sash should be at least five feet from the ground, 
and constructed for proper ventilation. The walls should be 
of a material which will allow proper disinfection. The floor 
should be of painted or washable wood, preferably of concrete, 
and so constructed that the floor may be flushed and properly 
disinfected. Proper heating, lighting, and ventilating facili- 
ties should be provided. 

94. In the event of any illness of a suspicious nature, the 
attending physician shall immediately quarantine the suspect, 
notify the health authorities and the secretary of the commis- 
sion, and examine each member of the dairy force ; and in every 
inflammatory afl'ection of the nose or throat occurring among 
the employees of the dairy, in addition to carrying out the 
above-mentioned program, the attending physician shall take 
a culture and have it examined at once by a competent bacteri- 
ologist approved by the commission. Pending such examination, 
the affected employee or employees shall be quarantined. 

95. It shall be the duty of the secretary, on receiving notice 
of any suspicious or contagious disease at the dairy, at once to 
notify the committee having in charge the medical supervision 
of employees of the dairy farm upon which such disease has 
developed. On receipt of the notice, this committee shall assume 
charge of the matter and shall have power to act for the com- 
mission as its judgment dictates. As soon as possible thereafter, 
the committee shall notify the commission, through its secretary, 
that a special meeting may be called for ultimate consideration 
and action. 

96. When a case of contagious disease is found among the 
employees of a dairy producing certified milk under the control 
of a medical milk commission, such employee shall be at once 
quarantined and as soon as Dossible removed from the plant, and 
the premises fumigated. 

When a case of contagion is found on a certified dairy it 
is advised that a printed notice of the facts shall be sent to 
every householder using the milk, giving in detail the precautions 
taken by the dairyman under the direction of the commission, 



320 PRINCIPLES AND PRACTICE OF MILK HYGIENE 

and it is further advised that all milk produced at such dairy 
shall be heated at 145° F. for 40 minutes, or 155° F. for 30 
minutes, or 167° F. for 20 minutes, and immediately cooled to 
50° F. These facts should also be part of the notice, and such 
heating of the milk should be continued during the accepted 
period of incubation for such contagious disease. 

The following method of fumigation is recommended : 

After all windows and doors are closed and the cracks sealed 
by strips of paper applied with flour paste, and the various 
articles in the room so hung or placed as to be exposed on all 
sides, preparations should be made to generate formaldehyde 
gas by the use of 20 ounces of formaldehyde and 10 ounces of 
permanganate of potash for every 1000 cubic feet of space to 
be disinfected. 

For mixing the formaldehyde and potassium permanganate 
a large galvanized-iron pail or cylinder holding at least 20 
quarts and having a flared top should be used for mixing therein 
20 ounces of formaldehyde and 10 ounces of permanganate. A 
cylinder at least 5 feet high is suggested. The containers 
should be placed about in the rooms and the necessary quantity 
of permanganate weighed and placed in them. The formalde- 
hyde solution for each pail should then be measured into a 
wide-mouthed cup and placed by the pail in which it is to be 
used. 

Although the reaction takes place quickly, by making prep- 
arations as advised all of the pails can be " set off " promptly 
by one person, since there is nothing to do but pour the formalde- 
hyde solution over the permanganate. The rooms should be 
kept closed for four hours. As there is a slight danger of fire, 
the reaction should be watched through a window or the pails 
placed on a noninflammable surface. 

97. Following a weekly medical inspection of the employees, 
a monthly report shall be submitted to the secretary of the 
medical milk commission, on the same recurring date by the 
examining visiting physician. 

The following schedule, filled out in writing and signed by 
himself, is recommended as a suitable form for the attending 
physician's report: 



APPENDIX 321 

This is to certify that, on the dates below indicated, official 

visits were made to the dairy, owned and conducted by 

of (indicating town and state), where careful 

inspections of the dairy emploj^ees were made. 

(a) Nmnber and dates of visits since last report. ■, 

(&) Number of men employed on the plant. 



(c) Has a recent epidemic of contagion occurred near the 
dairy, and what was its nature and extent.? . 

(d) Have any cases of contagious or infectious disease 
occurred among the men since the last report.'' . 

(e) Disposition of such cases. . 

(/) What indi^ddual sickness has occurred among the men 

since the last report.'' . 

(gr) Disposition of such cases. . 



(k) Number of employees now quarantined for sickness. 



(i) Describe the personal hygiene of the men employed for 
milking when prepared for and during the process of milking. 

(j) What facilities are provided for sickness in employees .? 



(A-) General hygienic condition of the dormitories or houses 

of the employees. . 

(I) Suggestions for improvement. , 



(m) What is the hygienic condition of the employees and 
their surroundings.? . 

(n) How many employees were examined at each of the 
foregoing visits.? . 

(o) Remarks. 



Attending Physician. 
Date, . 



INDEX 



Abortion, infectious, 116 
Acid- forming bacteria, 51 
Acidity, determination of, 254 
Acidity test with) Babcock 

pipette, 256 
Actinomycosis, 102 
Adulteration, detection of, 249 
Adulteration, determination of 

degree of, 246 
Aerator, 182 
Age of milk, 64 
Aggressins, 45 
Alcohol test, 285 
Alkalies, test for, 260 
Anaerobic bacteria, 57 
Animal-like taste, 28 
Anthrax, 100 
Antibodies, 42 
Antiformin method, 277 
Aphthous fever, 9^ 
Arnold's guaiac test, 298 

Babcock test, 233 
Bacillus abortus 116, 117 

aerogenes, 56 

bulgaricus, 54, 55 

coli, 56 

Guillebeau, 54 

lactis aerogenes, 53, 56 

lactimorbi, 104 

mesentericus vulgatus, 60 

proteus vulgaris, 61 

pyogenes, 108 

subtilis, 60 

typhosus, 121 



Bacteria, acid- forming, 5 1 

alkali-forming, 6l 

anaerobic, 57 

common-milk, eifect of heat 
on, 209 

counting, 260 

gas-forming, 55 

inert, 61 

of milk, 50 

pathogenic, effect of heat 
on, 204 

peptonizing, 58 

proportion of different 
groups, 64 

variations in number and 
kind, 62 
Bactericidal action of milk, 43 
Bacterium acidi lactici, 53, 54, 
55, 56 

lactis acidi, 52 
Bedding, 178 

Benzoic acid, test for, 259 
Beet-like taste, 71 
Biorization, 222 
Bitter milk, 69 
Bitter taste, 28, 29, 30 
Black scab, 100 
Blood in milk, 113 
Blue milk, 71 
Borax, tests for, 257 
Boiling test, 284 
Boric acid, tests for, 257 
Burnt taste, 30 
Burnt taste and odor, 71 
Butyric acid bacteria, 57 
323 



324 



INDEX 



Calculation of total solids, 241 
Casease bacteria, 58 
Casein, 14< 
Catalase, 38 
Catalase test, 287 
Catarrhal mastitis, 105 
Cells, number of in milk, 34 
Cellular content of milk, 34 
Certified milk, 46 

methods and standards, COS 
Clarification, 175 
Clarifier, 175 
Cleaning milk vessels, 189 

the cows, 166 

the stable, method of, l60 
Cocci, udder 59 
Coli-aero genes bacteria, 55, 56 
Coli, examination for, 275 
Color, examination of, 227 
Color, of milk, 28 
Coloring matters, examination 

for, 301 
Colostrum, bactericidal power, 13 

change of to milk, 13 

chemical properties, 1 1 

ferments or enzymes, 12 

judgment of as food for 
man, 13 

microscopic appearance, 12 

reaction, 12 

physical properties, 1 1 
Common milk bacteria, 50 
Composition of milk, variations, 

19 
Consistency, examination of, 227 
Cooked taste, 30 
Coolers, types of, 182 
Coolers, conical, 183 

corrugated, 183 

double-tube, 1 86 

internal, 186 



Coolers, regenerative, 219 

tubular, 184 
Counting bacteria, collection of 
samples, 260 
microscopic method, 267 
plate method, 262 
Covered-top pail, 172 
Cows, examination for cleanli- 
ness, 148 
for symptoms of dis- 
ease, 150 
Cow fly, 164 
Cow-like taste, 66 
Cowpox, 97 

false, 99 
Cows, stage of lactation, 149 
Cream layer, 17 
line, 17 

line, effect of heat on, 213 
Cubic air space, 136 
Curdling, premature, 68 
sour, 1 5 
sweet, 1 5 

Dairy Farm Inspection, 126 
Decomposition products, effect 

of heat on, 210 
Diastase, 37 

test, 297 
Dilution, effect of on infected 
milk, 73 
influence of on tuberculous 
infection, 86 
Diphtheria, 123 

bacilli, effects of heat on, 
205 
Direct infection, 72 
Dirt, examination for, 299 
Disease, influence of on milk, 72 



INDEX 



325 



Diseases of cattle which may 
render milk harmfiil, 104 
of cattle transmissible 

through milkj 73 
of man transmissible through 
milk, 119 
Doane-Buckley Method, 282 
" Dry " cows, 3 
matter, 19 

Electricity, 222 

Electrical conductivity of milk, 

34 
Enteritis, septic or hemorrhagic, 

114 
Enzymes, 12, 36 
bacterial, 37 
original 37 
effect of heat on, 213 
Examining milk, methods of, 223 
Excretion of medicines through 
udder, 119 

Failure to Sour and " Butter," 70 

False cowpox, 99 

Farrington's alkaline tablet test, 

256 
Fat, 16 

per cent., determination of, 
233 

per cent, in total solids, de- 
termination of, 246 
Feed boils, 100 
Feeding, 175 
Ferments, bacterial, 37 

effect of heat on, 213 

original, 37 
Fermentation-reductase test, 296 
Fermentation test, 278 
" Fishy " milk, 67 

taste, 29 



" Flaky " milk, 107, 109 
Fleshy udder, 3 
Flies, 161 

cow fly, 164 

horn fly, l64 

house fly, 162 

stable fly, 165 
Formaldehyde, tests for, 258 
Foot and mouth disease, 96 
Foul and unpleasant odor and 

taste, 29 
Freezing point of milk, 33 
" Fresh " cows, 4 
Fritzmann's Method, 248 
Furunculosis of the udder, 99 

Gas-forming bacteria, 55 
Gerber test, 237 
Germicidal action of milk, 43 
Gravimetric method for deter- 
mination of total solids, 240 
Greenish-yellow spots, 71 
" Gritty " milk, 68 

Hay bacillus, 60 
Heated milk, tests for, 298 
Holder and pasteurizer com- 
bined, 220 
Holding tank, 219 
Homogenized milk, 17 
Horn fly, l64 
House fly, 162 

Ice, quantity required, 187 
Indigestion, 114 
Inert bacteria, 61 
Infection, direct, 72 

secondary, 72 
Inflammation of the udder, 104 
Influence of disease on milk, 72 
Immune bodies, 42 



326 



INDEX 



Inspection of dairy farms, 126 
Interstitial mastitis, 109 
Intestinal tuberculosis, diagnosis 

of, 95 
Involution, 2 

Lactalbumin, 16 
Lactation, physiology of, 1 

stages of, 3 
Lactoglobulin, 16 
Lactometer, Quevenne's, 228 
Lactose, 18 

test for, 301 
Lactoscope test, 239 
Leach's test, 259 
Legal standards, 23, 24, 25 
Leucocytes, estimation of num- 
ber, 281 
" Letting down," 7 
Litmus test, 254 

Malt-like taste and odor, 71 
Manure-like odor, 30 
Mann's acidity test, 254 
Market milk, classes or grades 
of, 45 
composition of, 22 
frequency of tubercle ba- 
cilli in, 73 
prevention of contamination 
vrith tubercle bacilli, 90 
Mastitis, 104 

catarrhal, 105 

interstitial, 1 09 

milk, harmful properties of, 

110 
parenchymatous, 108 
tuberculous, 81, 93 
Medicines, excretion through 

udder, 119 
Metritis, septic, 115 



Milk, opacity of, 18 

biological properties, 36 

cellular content, 34 

chemical properties, 14 

color, 28 

defects, 66 

electrical conductivity, 34 

ferments or enzymes, 36 

freezing point, 33 

odor and taste of, 28 

pails, types of, 172 

physical properties, 28 

reaction, 26 

refraction, 32 

secretion, phases of, 6 
first phase, 6 
second phase, 7 

sickness, 104 

solids, 19 

specific gravity of, 30 

surface tension, 33 
Milk house, apparatus, 182 

construction, 181 

location, 180 

water supply, 193 
Milk vessels, methods of clean- 
ing, 183 
sterilization of, 190 

viscosity, 33 
Milking machines, methods of 

cleaning, 192 
Milking, methods of, 168 

Nauseating taste, 30 

Nitrates and nitrites, tests for, 

247 
Nutritive properties, effect of 

heat on, 211 

Odor, examination of, 227 
Odor and taste of milli, 28 



INDEX 



327 



Odors, absorption of by milk, 29 

CEdema of the udder, 113 

Oily taste, 30 

Opacity of milk, 18 

Open Tuberculosis, diagnosis of, 

94 
Orange-colored spots, 71 
Original contamination, 63 
Ozone, 222 

Paratyphoid fever, 123 

Parenchymatous mastitis, 108 

Pasteurization, 203 

" flash " process, 214 
continuous process, Sl^ 
"holder" process, 214 
in final container, 214 
methods of, 214 
principles of, 204 
summary of effects of, 213 

Pasteurizers, types of, 215 

Peptonizing bacteria, 58 

Per oxydase, 38 

Peter's test, 259 

Physiology of milk secretion, 1 

Potato bacillus, 60 

Premature curdling, 68 

Preservatives, tests for, 257 

Rabies, 101 
Rancid milk, 67 

odor and taste, 30 

taste, 28 
Reaction, determination of, 254 

of colostrum, 12 

of milk, 26 
Red milk, 71 
Reductase, 39 

test, 294 



Refractive index, 32 
Refraction number, determina- 
tion of, 250 
Regenerative cooler, 219 
Remont's test, 259 
Retained placenta, 116 
Retarder, 220 
Richmond's test, 258 
" Ropy " milk, 69 
Rosolic acid test, 260 

Salicylic acid, test for, 259 

Salts, 19 

Salty, cow-like taste, 66 

taste, 28 
Samples, collecting, 223 

individual, 226 

mixing, 226 

preserving, 224 

stable or herd, 225 
" Sandy " milk, 68 
Scarlet fever, 125 
Score cards, 197 
Secondary infection, 72 
Secretion of milk, first phase, 6 
phases of, 6 
physiology, 1 
second phase, 7 
Septic sore throat, 124 
Slow-creaming milk, 67 
" Soapy " taste, 70 
Solid's, determination of, 240 

by automatic reckoner, 245 

by calculation, 241 

Gravimetric method, 240 

determination of specific 
gra\dty of, 246 
Solids not fat, 19 

determination of, 245 
Sore throat, septic, 124 



328 



INDEX 



Sour curdling, 15 

odor and taste, SO 
Soxhlet's test, 24-7 
Specific gravity, determination 
of, 228 
of milk, 30 

of milk solids, deter- 
mination of, 246 
Spoiled feed, effects of on milk, 

114 
Stable, ceiling, 139 

drop, 144 

exposure, 129 

exterior, 129 

feed trough, 143 

floor of stall, 144 

gutter, 144 

interior construction, 139 

light, 146 

location, 1 29 

manger, 143 

odor of air, 131 

platform, 1 40 

ties, 145 

type, 129 

walls, 139 

stall divisions, 145 

stanchions, 145 

surroundings, 130 
Stable fly, 165 
Stable-like odor and taste, 29, 30 

taste, 71 
Stable practices, 159 

bedding, 178 

cleaning the cows, 166 

cleaning the stable, l60 

feeding, 175 

milking, 168 

time required, 179 
Stages of lactation, 3 



Stalls, arrangement of, 145 

hospital and maternity, 146 

Standards, legal, for milk and 
cream, 23, 24, 25 

Staphylococcus pyogenes, 59 

Sterilization of milk vessels, 190 

Stewart's test, 281 

Stokes' test, 281 

Storch's test, 298 

Strainers, 173 

Streptococci, examination for, 
272 
of mastitis, 53 

Streptococcus lacticus, 52, 54, 55 
pyogenes, effect of heat on, 
205 

Stringy milk, 69 

" Strippers," 5 

Structure of udder, 1 

Surface tension of milk, 33 

Sweet curdling, 15 

Taste, efl^ect of heat on, 213 
examination of, 227 
and odor of milk, 28 
Temperature, effect on growth 

of bacteria, 63 
Total solids, 19 

determination of, 240 
Toxins, 44 
Trembles, 104 
Trommsdorff test, 282 
Tubercle bacilli, 

from cattle, virulence 

of, for man, 75 
conditions under which 
milk is infected with, 
81 
efi"ect of heat on, 205 
examination for, 275 



INDEX 



329 



Tubercle bacilli, frequency of in 
market milk, 73 
human type, in milk, 

125 
influence of dilution on, 

86 
prevention of contami- 
nation of market milk 
with, 90 
Tuberculosis, intestinal, diagno- 
sis of, 95 
open, diagnosis of, 94 
of the udder, diagnosis of, 

94 
uterine, diagnosis of, 95 
Turmeric test, 258 
Turnip-like taste, 71 
Typhoid fever, 121 

bacilli, effects of heat 
on, 205 
Toxins, effect of heat on, 210 

Unclean taste, 30 
Udder cocci, 59 

diagnosis of tuberculosis of, 
94 

fleshy, 3 



Udder, inflammation of, 104 

oedema of, 113 

structure of, 1 
Ultra-violet rays, 222 
Uterus, diagnosis of tuberculosis 
of, 95 

Variations in composition of 
milk, 19 

causes of, 20 
Ventilation, 132 

cloth method, 135 

King system, 132 
Villier's and FayoUes' test, 257 
Virulence of tubercle bacilli 

from cattle for man, 75 
Viscid milk, 69 
Viscosity of milk, S3 
Violet-colored spots, 71 

Water, 19 

supply, 193 
Westphal balance, 229 

Yellow spots, 71 
Yellowish-green milk, 71 
Yellowish-green spots, 71 




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